I think that’s an interesting question. Walker Percy, in his Lost in the Cosmos, imagines a future Pope (abbot of a Benedictine community, but he’s basically the only possible Pope left standing after most of the world is wiped out in a nuclear holocaust) refusing to leave earth because that’s where Jesus is going to return. On the other hand, Walter Miller’s Canticle for Leibowitz (clearly a source for Percy’s sci-fi excursus in Cosmos) ends with the Church sending missionaries into space as a nuclear holocaust erupts.
Both Percy and Miller were lay Catholic writers of fiction and don’t speak for the Magisterium, though I’d probably bet more on Percy’s theological astuteness than Miller’s.
As far as I know, the question hasn’t been addressed officially. I think that the key would be how one understands “earth.” A good case can be made, I think, that “earth” means something like “created physical universe” rather than a specific planet. But I could be wrong. I certainly love the ending of *Lost in the Cosmos, *which contrasts the ragtag bunch of Catholics, Baptists, Jews, and drunken unbelievers hanging out on earth with the secularist paradise established on one of Jupiter’s moons. . . .
Edwin