GL Corps wiped out and Oan energy sucked into a small little battery pack which Galactus henceforth carries around with him for quick-snack purposes.
what happens if Galactus decides to consume all - ALL - the Oan energies?
will the GLs be able to manipulate the source of their powers better than Galactus? I doubt it.
fine, he wipes out the Guardians in the first nano-second with a galaxy destroying blast, thereafter he feeds on the remaining Oan energy.
or he feeds on the Oan energies and weakens The Guardians. given that he can feed on Hyperspace and consume The Celestials, I'll wager that he'll make light work of them.
even Surfer can manipulate and channel all the energies of the Oan Central Battery, Galactus would do so much more.
I think under the circumstances (namely the Guardians being involved), Galactus is going to take a loss unless he manages to consume a Guardian before continuing the fight, in which case he could take a win. If he doesn't consume a Guardian / Central battery or what-not, then he simply won't have enough energy to survive. The fight could go either way. Most of the 7200 GLC ring bearers will be fodder.
how resistant are The Guardians to a determined Galactus?
he annihilated a Watcher and untold number of powerful beings with but a mere blast - a blast that raged through galaxies.
I just honestly don't rate the GLC that highly, they're like low to mid-heralds at best, and the Guardians are just a few notches better. Galactus on the otherhand has creations that are superior to the Guardians (Tyrant) and he's never/rarely even bothered to demonstrate the heights of his powers, instead just trundling along doing just enough to get-by.
what would happen once Galactus started consuming the Oan energies? could the GLC/guardians do anything, offensively, against him? could they resist being made into heralds of Galactus? having their minds wiped, their willpower subordinated to his? having their rings transmuted to tofu sandwiches?