Ooh, toughie. Okay, I think Wolf would be more prioritized.
I personally believe all three will be back, but Falco and Wolf are no shoe-ins. That being said, if one of them had to go, I would say it should be Falco. And being a veteran doesn't do jack-diddly-squat. Falco is the cloniest of the two of them. And, on top of that, Wolf is a different fighter (he feels really different playing as him), and important to the franchise. The villain is more important than the sidekick. In fact, here's the breakdown:
Main Hero (Fox) > Main Villain (Wolf) > Sidekick (Falco) > Love Interest (Krystal) > Everyone else.
If we were brought down to two SF characters, I think it should be Wolf and Fox.