[logfromblammo]

Then we will either be literally extinct or at least economically extinct--permanently unable to recover space-launch technology. Then Earth has to gin up another dominant species capable of reaching the stars with whatever time it may have remaining.

We already have the technology to reach outside the solar system. It launched in 1977.

We will have the capability to transplant microorganisms to extrasolar planets long before moving humans that may have 100kg or more to one. Which is good, because it may take a while for the algae to get established anyway. And if for some reason higher species never show up, that celestial object won't have to overcome the steep initial hurdle of abiogenesis.