Second that -
I think the real reason why Imoen can be resurrected is that in BG1, Charname was the only Bhaalspawn in the party. Then came BG2, Imoen was made Charname's sister and a Bhaalspawn herself, but BW didn't bother to think about the implications. When ToB came, they had no reason to care about Sarevok either. At this point, the reason for "game over when Charname dies" was of very minor importance (it is never explained in BG2, so player's who didn't play BG1 had almost no hint at what's happening in the "dissolving hand" scene).
Catalyst: I feared that solution wouldn't be very popular.
Barring gameplay inconveniences, however, I really think it would be the best solution to keep the story consistent.
Though I don't expect that the idea will make it into IWG (or other mods, if I don't write one myself).
Caedwyr: On my computer, she tends to stay alive. B)