However badly we might treat our planet, it will almost certainly be easier to fix Earth than to terraform some distant dead planet. And if we do destroy Earth, from where would we get the resources to build the gigantic spaceships we would need to carry us away? (There would surely not be possible for us all to go.) So I don't believe we will leave Earth because we have plundered all it's resources.

But if we care enough for our planet to preserve it's environment, wildlife and resources, as well as all it's people, then I think some of us will eventually "set sails" for distant stars. I don't think it will be difficult to recruit volunteers either. But we will have to wait a couple of centuries before the technology is ready. And by then, we will know how to make the journey comfortable too, so that the lucky ones won't miss oceans, mountains, rainfall, etc. all too much (we already get most of our wildlife experiences from films, book, magazines, TV, anyway).