Firstly, if SWP&E bought Six Flags, the whole company, it wouldn't change the name, just things will be worked on. If they bought just one park, they would probably do a redesign of the park. There would be the same basic parking foundation and such but most rides will be renamed and redone, the buildings would probably be torn down and remodeled, and pathways reconstructed. A lot of work would go into renovating this old amusement park into a new theme park. I don't think it would be a Busch Gardens personally because Busch Gardens W and T are both extremely themed to continents that have very meticulous details, which would require 1) A new continent to be themed to and 2) A heck of a lot of theme work to be done.
Previous Busch Gardens parks that have been discontinued were themed after Asia, a typical idea, but not too accepted by the public apparently.
Come on Atlantis, play the "What if" game.