I'm torn at this point. On the one hand, I'm very tempted to let them suffer the negative consequences of their actions, as, depending on who opens the sarcophagas and takes the item in question, it could wreak serious havoc on the party. I'm somewhat annoyed at the fact that they wouldn't take the hint and turn back when things got much harder than they should have been. But at the same time, they were doing an exceptional job of working as a team-- far better than I've ever seen them do-- and of thinking their way past these obstacles. So I think they deserve to be rewarded as well. But if they manage to successfully acquire the item in question, they have no idea what it does, and, due to its nature, they'd have a very difficult time finding someone who did, so they'd have to sit on it until they were close to the level they should have acquired it at in the first place. I'm still deciding what sort of consequences to dish out, but I'm wondering what y'all do when you've got players that bull ahead on things when it should be fairly clear that they should turn back.
Incidentally, in cases like this, if the characters get killed, I have no sympathy, and let them die-- however, they played it very well, and though I got the fighter down to 1 HP at one point, that was the closest I can to killing a PC.