I love a bit of tennis, but it's mental how disinterested I've been with the US Open this year. That's in large part to Murray not participating, and probably an indicator as to how much attention I pay to tennis when he jacks it in.
It would have been top notch to have Murray and Djokovic compete with Rafa and Roger given the latter pairs resurgence this year.
To the OP's point, a good decision by Murray. Nothing to be gained by rushing back for year end. Get fit and healthy, have a good training camp in Miami over the winter and come back for the Australian.