On the other hand, I've heard that if you kill a plot-critical NPC, the game ends and tells you not to do that
I know some people thought they killed her because she leaves some items behind when she teleports away. Even so, the cave entry should be open after she leaves.
Of course, given the game's bugginess, one is never really sure of these things. Best bet is probably to restore and try this encounter again.
Nightowl2