Considering the excessive hassle that would be involved in getting your Dark Eldar ressurected by a Haemonculi, I don't think it would be against the spirit of the rules to let the players go for it. Because it's going to be a group effort afterall. Though depending on in-game circumstances and the whims of the GM, they might just let you defer payment until after the Dark Eldar is back up and breathing.
Of course, that still leaves everyone the whole adventure of getting to that point.
I'm even thinking of having my Dark Eldar character get one of the other party brought back, if they should die. After all, it should hardly be a test of a Haemonculi's skills to bring back as paltry a life form as the mon-keigh. Heh heh heh.. Trueborn cunning at its finest.
And sorry for snapping before Navi, got overdefensive of the game, but it's been my experience that when people start obsessing over idiot/abuse proofing every single rule and rule combination, the game can get bogged and, and just have the fun sucked out of it. Soon enough you'll have people pushing for a 100% simulationist style optimization focus be put on the game (most of the other changes are great, it's really just this ****, with Exalted).