I realize this could be its own thread, and maybe there's just never going to be any closure on this because it involves existing companies (perhaps with some of the same people still attached) who won't want to talk about it anytime soon, BUT...
I'm very skeptical of the whole "GW and Hasbro went to war" theory mentioned as fact by fans (including myself for a time) that is almost as old as HeroQuest itself. Maybe somebody on the inside "knows" and can't talk about it, but were the companies really at odds? Looking at the timeline I see that Milton Bradley (at the time a wholly owned subsidiary of Hasbro later known as Hasbro Games I think) worked with GamesWorkShop ("Citadel" being the catalog and line of wargaming miniatures they owned and were creating for Warhammer Fantasy Battle and Warhammer Fantasy RPG) for 1989's HeroQuest released first in the UK and then the rest of Europe and several other territories (including North America) the following year. 1989 also saw the release of "Advanced HeroQuest" which had no mention of MB on the box (I guess people interpreted this as evidence of some kind of "snub" or "rupture" between the two companies, rather than just that this was meant as a further transition into the realm of Citadel collecting, etc?). The same year the EU editions of KK and ROTWL came out.
"Hasbro Bradely" was the name given to the copyright owner of the Dave Morris HeroQuest novels (which of course had nothing to do with GWS other than an acknowledgment that the HeroQuest world was loosely based on the Warhammer fantasy world of GWS. (do people take THIS as evidence of a rupture? not the way Dave Morris tells it on his blog... he acted as if originally he was given free reign to create his world but over time they gave him more Warhammer stuff, making his original geography nonsensical and contradictory, the compromise being the world map he has is a distorted version of a portion of the Old World map featured in AHQ and on the back cover of the original ROTWL book from '89). But warhammer terms are still being used throughout the novels (even if there doesn't seem to be much talk of Chaos Warriors and no mention of Zargon... Zargon being an entirely NA thing... there is a "Morkar" in Warhammer but he's a Chaos Warrior from long ago, as opposed to a contemporary evil wizard).
Warhammer miniatures and terminology were used in all the expansions... 1991's NA edition of KK & ROTWL, Against the Ogre Horde and Wizards of Morcar in the EU (1990 and 1991, if I recall correctly). 1992's NA (or US only according to some) EQP and BQP used GWS assets once again (the mercenaries in the Barbarian pack, the Ogres in the Elf pack, and the cancelled Dwarf pack was going to use the other three Ogre designs while the cancelled Wizard pack was going to re-use the WOM bad guys). The card artwork would even have borrowed some designs from the cards of the EU packs (ATOH/WOM). Even though the new miniatures were being created by someone outside GWS this time (if I recall the notes correctly, lucapaschi can confirm) they were still using Citadel miniatures in 1992 (and possibly would have in 1993 if it took them another year to finish those other two hero themed expansions).
Legacy of Sorasil was a computer (and console ported to the ill-fated Amiga-CD 32) game from 1994 but other than having HeroQuest in the title and a set of heroes that is clearly based directly on the four from the original game (as well as featuring cover artwork that depicts those heroes very close to the Les Edwards type designs seen back in 1989), it bears little resemblance to HeroQuest and could be any other generic (or D&D inspired) dungeon crawler game (now with outdoor areas too!). The Talisman of Lore makes an appearance but otherwise its very tangentially related to HQ and didn't have any physical board game equivalent. Being a digital product obviously there was no connection to GWS here. Is that what people are assuming that the two companies had parted ways? But think of how late in the HQ lifespan that is. Two years after EQP/BQP. I could imagine if such a rupture took place between the companies it must have happened around '92, because it seems they are honoring some kind of agreement up until that point with the designs and terminology being used. EQP changed to "Quest Pack for the Elf" due to a lawsuit from the owners of "ElfQuest" (a series of comics from the 70's and 80's).
Back to Advanced HeroQuest. You could say this was an attempt to draw HQ players away from the MB game and into the world of collecting, painting and playing Warhammer games (even before Warhammer quest, which came out in 1995, quite a bit after AHQ... was this proof of a "final rupture" between the companies, not counting the time they collaborated on "Warhammer 40,000 Risk" in 2020? Granted, that was through publisher Usopoloy aka "The OP" considered a "small business" that makes those "themed" versions of Monopoly sets.
Advanced HeroQuest included optional rules on using the various assets from MB HeroQuest IN Advanced HeroQuest! This was similar to how White Dwarf (the official magazine of GWS) included custom HeroQuest adventures (and always the lure of using specific Citadel miniatures in these new adventures alongside the HeroQuest assets!).
Recall that White Dwarf had two issues (both from 1991) in which they featured the adventures "Halls of Durrag Dol" (#134) and "The Eyes of Chaos" (#145).
Who the heck are "Usopoly"? At first I thought maybe it was another Hasbro subsidiary but they say about themselves:
We are The Op Games | usaopoly, a leading developer and manufacturer of board games and puzzles. We've been producing the world's most beloved games "with a twist" under license from Hasbro, since 1994.
Risk, Monopoly and Clue are well known Hasbro properties.
Looking other places, MB and GWS collaborated on the (EU only) "Space Crusade" (aka StarQuest) that made extensive use of the Warhammer 40K lore (modified in the German "StarQuest" variant in terms of text lore at least in the core set, but with little change in the two expansions and certainly still making full use of the art and sculptures of GWS for the figures).
Hasbro worked with Takara (a Japanese toy company) to make the Japanese edition of the HeroQuest game system in 1991, and while changing the names of many things (Dark Warriors, Monolizards, Grimdead, etc) and using a different world map (the Island of Neef, obviously a riff on Nippon, aka Japan!) much of the old GWS art was still included and the miniatures were all included in all their GWS glory.
BattleMasters was a clear collaboration between MB and GWS in 1992. Not only were the miniatures all GWS but the lore used terms tied in to the Warhammer fantasy world, fleshing things out a little more than even HQ did. They used brand new sculpts of many things, implying they weren't just cruising on the fumes of some old contract that let them use the HeroQuest minis. No undead figures but plenty of Chaos creatures, greenskins and of course the brave men of the Empire. It saw EU and NA releases (the expansions, which really only recycled miniatures from the core set with some new stickers for the flags/heralrdy) appeared shortly after but in the EU only.
The official computer games for HeroQuest (1991, re-released on CD-ROM in 1995) and Space Crusade (1992, 1995) were done through Gremlin (formerly associated with Sega, way back in the day), without requiring any involvement from MB, but interesting enough the official rules for the board game versions of both games are included (in abbreviated summary) inside the instruction manuals of both digital incarnations of these games! Space Crusade on the computer was more altered from its board game incarnation than HQ (which while based primarily on the 1989 game plus Return of the Witch Lord mostly just had really poor enemy AI and let the Wizard use everything, which was fine since they left out the Cloak of Protection and had the weaker form of the staff seen in the NA edition; the unreleased NES/Famicom port of this game while only featuring 2 heroes in a game at a time, was going to include all assets from the EU edition plus Kellar's Keep alongside ROTWL, pity it exists only in prototype form). The mazes were much larger and had different arrangements, the GeneStealers were altered into Xenomorph looking "soul suckers" but other GWS artwork and designs were clearly retained. "The Voyage Beyond" available either as an expansion (sadly only to Atari ST and Amiga versions of the computer game) or as a combo pack with the based game (again only on atari st and amiga computers) was released later in 1992. It included Space Ogres that strongly hint of the "Ogryn" from 40K as well as the "Mother sucker" (I'm not joking, that's really what it is called) that bears a strong resemblance to the xenomorph Queen from "Aliens." (the Genestealers and Tyranids all are reminiscent of the HR Giger designs for Alien anyway).
So what was this "rupture" between the companies? What form did it take? A few lines of dispute or beef have been posted between the former head of GWS (Brian Ansell) and Stephen Baker (but all coming from the former; Baker recall worked at least briefly for GWS, but the basic lore in a lot of old interviews is that Baker "invented" the game while the contention of the other is that GWS basically re-created it after Baker's designs proved unworkable; nowadays Baker retains a good relationship with Hasbro as a semi-retired kind of contractor or advisor, I don't know what Ansell is doing, and any drama that might exist between these men isn't that interesting to me, honestly) have surfaced in the past few years, but other than some kind of professional jealousy or friction that might be evoking, I don't see any obvious proof that the two companies were at odds or some kind of dramatic fight over the HQ property. If such a "VH-1 Behind the Music" scene happened, it seems to have been covered up very well.
Avalon Hill wasn't involved in the original HeroQuest, but the company we know today (which again, is a subsidiary) originated in 1998, after (according to wikipedia) the old gaming company was acquired by Hasbro and the entire team was replaced.
Though it has little bearing on anything, the HeroQuest title (at least) was owned for a brief period by Chaosium for their "Glorantha" game that I believe was renamed HeroWars (this I know a lot less about) and that's what the hullaballoo was about around the time the 25th anniversary edition (now known as the ill-fated TseuQuesT which is currently in a legal case last I checked) over who owned the title (and that's clearly now Hasbro, Inc).
We only heard a little suggestion that there was "resistance" to the idea of remaking Space Crusade at this time, apparently coming from both companies but we don't know exactly why, not much else.
I could only speculate and imagine that GWS's goal is still to push their miniatures and if they don't think that will happen they won't do it. But they have certainly branched out and are selling lots of small packs of stand alone (or one off) type boxes (I guess some of these have had sequels) like Killteam, Fireteam, Space Marine Adventures, and they've remade Space Hulk (the original predated Space Crusade) too.
This is what I've learned just searching the web, so while you can't trust everything you read online, perhaps someone else can shed light on this?