He’s just lurking around in the MCU just like Abomination, Leader, the Mandarin, scorpion, vulture and a lot of other MCU villains that made only one appearance and they didn’t die yet?
Banner mentioned in Infinity War that Vision's consciousness is comprised of multiple identities including Ultron. So yes, a part of him exists. As far as a full resurrection of the character, I think the chances are slim.
