The Exile like said draws from the Jedi Masters when they are weak and defeated...
The bond between Kreia and the Exile is destroyed not because Kreia goes Dark but because she destroys it or because the Exile is complete again and can no longer draw from his friends. Basically meaning he is just him nothing more and he still manages to beat Kreia.
And yes i do agree that Kreia would know Revan, but she has not trained him for a long time. She says he sought her out before and after. Before probably being the Mandelorian wars, and we all know Revan has learned a lot in those wars and has trained with many Masters, so Kreia could not know everything about him. After probably means when Revan sought her out to find a way to kill Nihilus. The two haven't seen each other during the Mandelorian wars or during the time Revan ruled as a Sith Lord. So Revan has learned a lot of new things, probably his own technique which you can see in Kotor I. And he has learned to duel with several different styles of lightsabers and two at once. Maybe he always could but i doubt it, and if he could then i doubt Kreia would know his moves with those things. Seeing as she didn't train him during the time he gained most experience and developed his style more and better.
Trust me i don't think Kreia is a push over, not even for Revan. But i am pretty 100% sure Revan could beat her before the Exile could beat Nihilus. Revan would stand up against somebody he would win from easily, especially seeing as the Exile has just been through a damn tough fight and is now standing up against somebody with more power skill and knowledge and who probably had less of trouble in the previous fight. The Exile would lose.
About the Nihilus thing, who says he can't draw from Kreia. He obviously draws from the Exile his companions on his ship, after all you kill the entire ship and the fool is still standing. There are some people there but they are weak and just soldiers. They are not enough to sub stain him let alone stand enough to make him win a fight against the Exile. So he does draw from Mandalore and Visas. When you still beat him however he tries to draw from you, and that is when he fails. Still he isn't weak he still has some power to draw from and does it.
That makes me believe he is more then able to draw from Kreia, he has a bond with her too, as you do. That Basically means he can stand up against the Exile. He probably has a little less power to draw from, seeing as the Exile will use most maybe they have an equal amount but i doubt it. The Exile would win because eventually Nihilus would be defeated by skill and then be stupid enough to try and draw from the Exile.
I don't think the fight between them is going to be over soon.
And all of this is assuming its going to be Revan vs Kreia and Nihilus vs the Exile, would it be the other way around then Revan would kill the Exile and Nihilus Kreia. Which would probably be a smarter thing for them to do, but far less fun to think about.