UTC is the atomic clock (TAI minus 37 seconds currently); UT1 is "Earth time". We would use UTC. UT1 would end up only being used by astronomers and whoever el

UTC is the atomic clock (TAI minus 37 seconds currently); UT1 is "Earth time". We would use UTC. UT1 would end up only being used by astronomers and whoever else cares about the Earth's rotation. By the time UTC and UT1 diverge enough to matter, humanity will have either destroyed itself or come up with a new time standard.