Without nearly infinitesimally cheap and nearly infinitely abundant power, leaving the Earth is going to be very difficult.

The planet is going to be here a long time. The Sun going into its Red Giant phase is going to eventually do it in, but short of that, it'll be here. That's around 5B yr from now. Before then, life will find a way to start over, if necessary.

Thinking about all of the changes in the last 10,000 years, I wouldn't be pretend to be able to predict out that far, let alone a few billion years. But we've got bigger problems now...

Maybe we should return to the sea. We wouldn't need any roads for transportation and that's a big plus. :-)

Cheers,
Scott.