re: Far earlier
"Long before the sun inflates into a giant red, our planet will have lost its liquid water (might happen in just a billion years from now)..But our species also can't stay this way for that long either. "
Now you are talking, let's do something about that shortage of water on Earth.
People shouldn't mistake my idea of exporting water off Earth as something that will add to our water shortage, but should think of it as using a tiny amount to prime the pump, or down payment of an investment in water.