Well, we all know that there will always be 'true-sith' because Anakin, Bane, Sidious ,ect. are 'true-sith'. So even if Revan destroys the 'true-sith', which I think would be the species, there will always be more of them, in a sense.
I think that we need to know what happened to Revan during his/her journey into the Unknown Regions. Since that in TSL, Revan was talked about leaving into the Unknown Regions, I think that there will be something about what a happened, at the least. I personally wouldn't mind if Revan wasn't the main character in KotOR 3, of course if it ever comes out, I just want to know what happened to him/her.