As cool as a former admiral in the SHs seems on paper (and its implications, like a future Aokiji x Kizaru fight, etc.), I don't think it'll happen. I feel that it would kinda imbalance the world, having so many admirals resigning. Plus, we already had an event of an admiral resigning and joining a Yonko crew (Aokiji), but it didn't seem to be "an incident that shocked the world" (it's apparently on par with the Payback War), as the one we expect to happen soon. Unless Saturn dies in the process, then that would be bigger than anything that ever happened since the One Piece was found.