... Pietro's actual involvement would depend entirely on how much Wanda cares. If she doesn't, he'll probably suggest running off to the first tropical country that comes to mind and letting everyone else deal. He's nice like that.

If she does make him stay -- Pietro is actually a rather skilled tactician and has done this whole war thing before, a few times, with a few different military unit-ish set ups. He's not opposed to working alone, and will if it comes to that, but he recognizes that his powers work best when there's some kind of team dynamic going on. If push comes to shove, he'd contact what's left of the Mighty Avengers and old X-Factor to try and get a team-up going and be very ticked if they told him to jump.

On the whole though, if Wanda ends up in danger somehow, that's where his priorities will be. Surprise, surprise.