For me, having them be blindsided by such a major disruption was at least half of the point of doing the crossover. (I posted it right alongside one in which their plans are instead derailed by the 1999 emergence of Lavos, and the subsequent devastation and mass death which follows.)
But if you don't want to do that, you certainly wouldn't have to. It would just result in a different sort of story.
But if you don't want to do that, you certainly wouldn't have to. It would just result in a different sort of story.