Revan...well it's supposed to be a mystery what happened to him. I have read all of the book. I have seen the spoilers in the game. Two very different things could happen and decide Revan's ultimate fate. Then again I am not altogether sure the 2 sides are exclusive of one another based off what I have seen. I'm not going to explain any further about Revan, go find out for yourself; I care not how. You'd want to play for the experience and social interaction obviously. The story is already posted up on youtube I'm afraid. If you just want to find out for interest's sake and don't care to play, then watch. If you would rather forge your own version of the tale, then play it out. Wookieepedia will try to reconcile things as it always does. Unfortunately only some events may be recorded as canon. I'm sure the rest has already been planned as to explaining the who, when, and what: expect a lot of "There seems to be a conflict of [at least two] accounts of just what happened or who did [insert event], in some cases it is jedi, in other cases it is sith".
TL;DR: Too many variables and contradictions to truly know *everything*. Some will be accepted for which there's no alternate, some won't. Others will be duly congruent or concurrent meaning both sides will have had their role.
Far as Revan:
he shows up again in some form,
but I don't wish to post spoiler videos.