Why wouldn't Spock at least try to return to the prime universe?
He has a (maybe still) wife, also perhaps children. Aside from the personal aspects he is the Federation ambassador to Romulas, with the massive destruction to the empire caused by the supernova, Spock will be needed more than ever. Spock has always been shown to be a very responsible person. It not like he wouldn't be able to come up with something. Just skip from one universe to another.