gravaillon wrote:perhaps it could be in war. the skaven nimh like and the GW skavens. So perhaps, the skaven nimh can become the allies of the heroes.
Could be a good solution of this problem, and could also solve the other problem that Ethica pointet out, all in one go:
The piper was kidnapped by the NIMH scaven, who wanted to keep him in control, as he is dangerous to them, too, but didn't want to kill him as they are creatures with a moral code, or searching for a moral code of their own, wanting not to loose the "humanity" they got (or, not to loose their "animality", considering murder an typical human act).
Or, to make things less brainy, they just want to be accepted by the "good" races and don't want to trouble the dipolytic relations to come by killing off the piper. So it's clear why the piper is held captive alive, although the heroes might wonder and find out only later. It also explains why the piper is in an completely other dungeon then the flute - he's kidnapped by a different tribe of scaven.
In the quest for rescuing the piper, the heroes could find some hints that something is strange about these scaven. You would, however have to find a reason why they don't negotiate with the heroes from the start. Simplest would be that they don't speak the human language. This would however make it very difficult to use their dramatic potential later...
Perhaps the heroes can fight their way to the inner dungeon where the piper is held, and met an old skaven sage there who can speak the human tongue. He explains the troubles of the "NIMH"-skaven, and they can become allies in a later quest.