The main issue with this is a week to the traveller crossing the galaxy near the speed of light still requires civilization to stay together for 100,000 years w

The main issue with this is a week to the traveller crossing the galaxy near the speed of light still requires civilization to stay together for 100,000 years without them. The second issue is it's not as attractive as it sounds. Travelling 1/10th the galaxy in a proper time of 5 days requires a trip of a constant 2400 G's. Maybe solvable once your civilization has already overcome the Fermi paradox (probably don't need bodies at that point) though.