If the Fall of Beacon does occur, I'd imagine that Robert would gather anyone he knew who hadn't gone lone wolf and try to track down each person one at a time. Because despite everything, he's an idealist and he believes that, with enough people, they could reclaim the place they used to call home. He wouldn't care if it took years to track everyone down, he wouldn't stop for anything, especially if gathering everyone means he'd get to see his friends again who he sees as the closest thing he has to family.