If comicbook stupidity is at play (in which case Galactus is very prone to fight them like a big, dumb, brick with energy projection), then the Kryptonians actually have a chance to win...
But sans comicbook stupidity, Galactus could defeat them all a million different ways...one of which I quoted above.
Galactus 10/10 without much effort sans a strong helping of PIS...
Aside from the aforementioned solar drainage, I wonder if the power stunt that Galactus pulled during the end of Annihilation would kill them all off, or at least thin out the herd, because if not, I think Galactus is going to be taking a major @$$ ripping in this one.