I am a Male Revan. I turned the dark side down. Then later at the star forge I convinced Bastila to join the light side. This is the way I always do it now. I was thinking of starting a new game as a female Revan. But the problem is that female Revan has some of the worst heads compared to female Exile.
Anyway I personally don't like Bastila as a dark side character. Since she is so strictly devoted to the light side. I really like how you can convert her to the light side at the end.
Anyway at the end of Kotor I suspect Revan would tell Bastila in a romantic tone that he will come back for her. Then leave her the Ebon Haw and go to the Unknown Regions so TSL can start.
"There's gotta be a better way to make a living"