Wow, you have a great assumption, but I think that if they were meant to be together, Katherine would have to pag-ibig him. But she doesn't care about him,and she never did. She was just using him and Stefan for blood and a low profile. When the secret got around, Katherine tried to cut to the chase and kill them both, which, along with breaking up the brothership, was her plan all along. And Damon is pissed at her and himself because he didn't see that before and he was looking all over for her, just to figure out the truth. And it doesn't matter anyway, because if Katherine cared enough to let Damon stop her from killing Elena, which would be hard because she is stronger than him,she would not have the strength to keep from biting her. Damon would still hate Katherine for brainwashing him and lying, so he would try to kill her in the process of saving Elena, or die trying, and then, so would Elena, because Katherine would go after her when Damon was dead. But because he hates her now, he would never let her get close enough to him, Stefan, or Elena to do so in the first place. When you watch the show, you come up with these answers. Bottom line is that they hate each other now, so if the do sa pamamagitan ng some very unfortunate chance see each other again, they will not be happy.