Re: next shichibukai?
They won't disband - why? Because Kuma being a "spy" doesn't work if he gets kicked out a few chapters after being hinted at being a spy.
Disbanding the Shichibukai would be like the WG shooting themselves in the foot. If you think the Shichibukai were just there to scare rookies and backup the admirals in a big fight, you are most definitely mistaken.
The Shichibukai exist because they allow the WG to manage pirates. Sure, eventually it would be nice to get rid of all pirates from the WG's viewpoint, however they exist. And whilst pirates exist, it would be silly to declare war on every single one of them. The saying "Keep your friends close and your enemies closer" is the exact reason the Shichibukai exist.
I'm sure, in their quite possibly long history, that 2 Shichibukai betraying at the same time is not unheard of. If you think the Gorosei are going to make public enemies of powerful pirates rather than turning a blind eye just because 2 guys changed their mind, you must think the Gorousei are a self-destructive bunch.
If you're playing Age of Empires, and you have 3 teams "neutral", no allies and 3 teams "enemy", you don't declare all neutral as "enemy" just because one neutral changed themselves. You also don't declare neutral as enemy just because you beat one enemy.
Tactics people. I've seen no-one mention a benefit of disbanding the Shichibukai other than hoping to not be betrayed again and instead be at open conflict with, doesn't sound like a great move to me.
On topic though: Any of the Supernova, though I expect Law, Kidd, Killer, Capone and Bonney escaped; Hawkins, Drake, Apoo or Urogue are all definitely captured and could make good Shichibukais. That said, if the two slots are instantly filled with 2 Supernova I'll feel a little disappointed because then the only two unrevealed sillouettes in One Piece are Kaidou + 4th Yonkou.
Also...would they be beneath reinstating Crocodile? I doubt they will, but it's an idea worth mentioning.