SPOILERS for the Legends of Tomorrow season 3 finale ahead
Legends of Tomorrow bids farewell to a teammate in the season 3 finale as one member of the Waverider crew dies in a heroic moment. At the start of the season finale, Rip Hunter (Arthur Darvill) sacrificed himself to buy the Legends time to escape from Mallus. Rip was a key member of the team, of course, being the one who assembled the crew way back in the Legends of Tomorrow series premiere. In season 1, he led the team against Vandal Savage, but Sara Lance assumed the captaincy of the Waverider in season 2 when Rip disappeared.
Rip has been around even less in season 3, which makes sense since he was a series regular in the first two seasons, but a recurring cast member in the show's third outing. Still, he and his Time Bureau brought Mallus to the attention of the Legends, and he eventually teamed up with them to fight against the demon. Now, however, Rip has sacrificed himself to save his team - seemingly signifying Darvill's exit from Legends of Tomorrow.
At the start of the Legends of Tomorrow season 3 finale, Rip removed the Waverider's time drive from its housing, causing it to become unstable and explode. This killed Rip and sent Mallus back in time, allowing the Legends time to regroup and figure out how to use the totems against the demon. Rip told Sarah, his successor as the leader of the Legends, before he died, "My one hope is that you all live up to that name." It was a poignant send off to one of Legends of Tomorrow's original team members.
Showrunner Phil Klemmer previously teased an exit from Legends of Tomorrow in the season 3 finale, and it certainly won't be the first (nor, likely, the last) time the team is shaken up thanks to one member dying or leaving the ship. In terms of Darvill's send off as Rip, Klemmer spoke to ComicBook about the finale and the character's arc throughout the show:
I will say that our love for Arthur Darvill exceeds our need for his character. Our reinvention of him last season was... We just felt we owed him a chance to do something different than what he had done season 1. I totally agree that he set things in motion and hopefully his appearance in the finale will... His appearances in the show, I think he was a reminder of just how far the Legends have come since the premiere.
Given Klemmer's comments, it seems unlikely Darvill will ever return to Legends of Tomorrow as a series regular. However, since this is a time travel series, the writers could find a way to have him pop up again in Legends of Tomorrow season 4. After the death of Leonard Snart/Captain Cold (Wentworth Miller) in season 1, the show brought back an earlier version of the character as a villain, then introduced an alternate universe version who went by the name Citizen Cold. Anything is possible in superhero shows - especially superhero shows with time travel.
Still, Rip's death in the Legends of Tomorrow season 3 finale may stick, though fans will be disappointed to see Darvill leave the show. At least Rip received a true hero's death, sacrificing himself for his team. It's an appropriate end to the character who brought the Legends together in the first place.
Legends of Tomorrow will return for season 4 on The CW.