Thor can in fact be killed. In the Ragnarok story line he and all the Asgardians were briefly killed. While Thor will probably never die of old age it is possible for him to die in battle. read more
Yes. If his father, Odin can die, so can Thor. They just live an awfully long time. Plus the Asgardians talk of how Earth’s people “assume” the immortality of them indicating it was not true. Thor is a younger Asgardian but he says that he is 1500 years old in Infinity War. read more