I agree with Kahuna Burger . this whole story sounds to contieved, with the only goal to set the PCs back. Could be that it is the mood of the campaign - struggle against all-but-hopeless- odds, but in a regular "beat then evil forces" campaign I'd be very frustrated as a player. There is sometimes a fine line between outsmarting the PCs (or players) and making it impossible for the PCs to achieve their goals.
Last adventure I played the DM brought a Blackgaurd back that had faced our party before (and almost killed our barbarian with a a mounted charge & smite good after torturing the rest of the PCs). The blackguard challenged the barbarian to single combat (after the barbarian had already taken some damage, and after downing a cure potion herself), but the battle itself was rather fair (with the exception of a deeper darkness used by the blackguard). In the end, the blackguard was brought to her knees (1 hp left) and begged for her life. Only after the barbarian had stopped the combat, talked a bit and then was picking up the evil lifestealing sword of his adversary did the blackguard jump out of the window on her nightmare to flee. If the blackguard had had a contingency or similar "fail-safe" escape it would have left the impression that no matter what she would have escaped. That way it was literally in the hands of the PC if she could escape or not.
I think, judging from the amount of information available, that a simple robbed (and possibly trapped) tomb might have been better to set the PCs back a bit.