He can – but he shouldn’t
Leaving aside the fact that his franchise has been, thus far, the weakest in the entire MCU, Thor shouldn’t continue being an Avenger after the Infinity Wars have ended.
The appeal of the MCU lies in this question: what happens next? For example, with Captain America, we saw him clashing with HYDRA, with the final confrontation being, most likely, during the Civil War. Iron Man has tricked us until now, leading us to believe that the Mandarin will be the final enemy of Tony Stark.
With Thor, Loki has always been a central character, who has never crossed the line into becoming a hero. So Ragnarok or the Infinity War might just bring the end of this clash.
But the charm of the MCU is always bringing something new to the table. The Infinity War will come and go, thus ending what could be called the Golden Age of the MCU. Even if Thor could remain in the Avengers roster, he shouldn’t.
Whether killed, whether King, whether going into seclusion, he should step aside and make way for other superheroes – and, thank goodness, there are still many of them in the comics.
