So, playing with the idea of the ball here is what I have come up with.

Damon and Klaus are invited back to Mystic Falls for a founders ball, and they bring along Cassie and Anya. I see them staying because the hunters after Anya are there and the others are protecting her.

I also see iy being the place that Cassie reawakens herself as a hunter.

I also see Damon and Klaus teaming up together to try and figure out the main plan of the hunting group. 

I also may take Cassie out for a few posts after she reawakens, give myself time to figure out how to work her out as a hunter.