I'm under the impression that the devs have said that Revan will play a vital role in KotOR II, thus Bastila will aswell. Please correct me if i'm wrong about this (with links or quotes ).
Forgot to add that part. Sorry.
A million things could have happened to Bastilla to prevent her from being with Revan.
I guess she should have looked both ways before crossing the street.
Maybe she tried to betray him (if Revan took LS, then she never fully became LS and fell to DS again...if Revan took DS, then it's only inevitable that she would try to eventually become Dark Lord of the Sith). In any case, I think all the characters can be unmentionable in the entire game, with the exception of Revan. Since he did do something with the Star Forge, there should be a mention of him at the least.