The closest thing you'll get is that MAYBE he'll be one of Xehanort's vessels, and he'll get tired of being Xehanort's errand boy, so he'll turn on him and work with the good guys exclusively to kill Xehanort, and then he'll fuck off and be the main villain of Kingdom Hearts 4.
Or he'll stay 6 feet under, where he belongs.
No offense, but the notion of anyone having any sympathy for the character whose whole point was being a enormous prick absolutely baffles me.
I've been thinking... Since I think Vanitas has gold eyes because of Xehanort... Maybe he has actually blue eyes like the others? I would be epic if in KH3 he manages to free himself and then his eyes would turn out to be blue.