My assumption is that you'll just choose which Primal you want to draw power from; no Fat Cats will be harmed. This does make me wonder if crystal-summoned non-primals like King Mog and Enkidu count (probably not but it's fun to think about)! And Bahamut being the method to suddenly cast Judgement Bolt or whatever makes me wonder how it'll happen story-wise, since I doubt they're going to assume everyone's cleared Final Coil.
