Or, and this sounds more on point for director Taika Watiti, they could’ve dumped Thor from their ship within minutes of his arrival, leaving Thor: Love and Thunder to pick up just after Avengers: Endgame, with Fat Thor still intact.
According to James Gunn, Thor: Love and Thunder happens before Guardians of the Galaxy 3, which leaves a lot of options on where Chris Hemsworth’s next Thor film will pick up in the hero’s life.
He could go on a whole adventure with the Guardians and arrive back on Earth a year later looking fit.