Well, Gerard has no way past KS. But Aizen might want to...test his power or something? Anyhow, once Aizen notices he can't bypass his Regenerationn normally, he might just place him under KS and stack binding Kido on him to incapacitate.
Otherwise, it's inconclusive, I guess. By the way, isn't this version of Aizen's best Regenerationn feat Low-Mid? If so, maybe Gerard could pull off a win if Aizen messes around, but I doubt it.