While character deaths are notoriously impermanent in the Arrowverse, so far Hunter’s departure from Legends of Tomorrow has proven to be final, although there is always the possibility that Darvill will return in the future.
Rip himself died at the end of season 3 of Legends of Tomorrow, sacrificing his own life to buy time for his team of superheroes in their fight against the demon Mallus.
Sometimes when actors leave a television show, contract disputes or a conflict is the explanation. In the case of Darvill’s departure from Legends of Tomorrow, it appears that Rip Hunter’s death was a creative choice.
There is always the possibility that Rip Hunter will return in future seasons of Legends of Tomorrow. Executive producer Marc Guggenheim said it was possible that Darvill could return as Rip Hunter.
Darvill met (virtually) with the cast members of Legends of Tomorrow. Legends of Tomorrow season 6 began filming in October 2020 and is expected to premiere in the spring or early summer of 2021.
Although there is no news of Rip Hunter’s return, a dead man coming back to life wouldn’t even be on the list of the strangest things to happen in Legends of Tomorrow, so fans can always be hopeful.