Suppose everything depends on which airfields survive. It's unlikely that the MoD will be able to justify the continuation of Yeovilton when there's hardly any helo traffic there and a very active base at Culdrose, and of course Yeovilton has already been ruled-out as a potential F-35 (or Typhoon) base (supposedly because the runway isn't long enough - funny how it was long enough for Phantoms and V-Bomber dets, but evidently not long enough for a new vstol aircraft!).
On the other hand, all of the FAA's top brass, past and present, probably lives much nearer Yeovilton, so you can imagine that there will be plenty of support and lobbying for keeping the airfield open for purely selfish reasons (not that I'd suggest for a minute that any Navy chiefs would act in this way *ahem*). But moving all of the helo assets from Culdrose would be politically-risky too, as it would inevitably destroy Helston's local economy and probably much more besides.
Logically, the best plan would be to close both airfields and hand-over St.Mawgan to the FAA, as it has a huge runway, a full shelter complex, an enormous servicing hangar, and a blossoming local airport which depends on MoD support (the council claim that they can't afford crash/rescue themselves). It would also be hugely expensive to return the airfield to its pre-use condition, and it probably has zero value as development land, because of it's "green" location. At least it would keep some jobs in Cornwall should Culdrose be disposed-of, but I don't imagine the idea would be too popular with Yeovilton!
It really is very difficult to predict what will happen with all three bases at present. Guess we'll have to wait and see, but it must be pretty unlikely that all three bases will survive.