Arthur Darvill’s time as Rip Hunter in the DC series, Legends of Tomorrow might not be quite as finite as it seems right now.
Consider the alumni of the Eleventh Doctor’s era: Matt Smith’s (the Doctor) most high profile post-Doctor Who job has arguably been The Crown; Karen Gillan’s (Amy Pond) has probably been as Nebula in the Marvel Cinematic Universe (MCU); and Arthur Darvill’s (Rory Williams) has undoubtedly been in Legends of Tomorrow.
But, spoiler alert in case you’ve not seen the Season 3 finale yet, his character sacrificed himself in The Good, the Bad, and the Cuddly.
However, that might not be the end for Hunter. Executive producer, Marc Guggenheim says:

“We love Arthur, we love having Arthur on the show, and I think Arthur enjoys being on the show. Because it’s a time travel show, and because we never saw a body, anything is possible. I think Arthur is totally willing to come back and play with us if we have a cool idea.”

Fellow executive producer, Phil Klemmer recently noted:

“I will say that our love for Arthur Darvill exceeds our need for his character… We just felt we owed him a chance to do something different than what he had done [in Season 1].”

Rip has been a vital part in the show – he was the reason the heroes (including the Atom, Captain Cold, Heat Wave, and Hawkgirl) were brought together, in an attempt to avert a possible disastrous future. Nonetheless, Hunter’s appearances have got fewer over the 51 broadcast episodes to date, and although he was somewhat reinvented for Season 3, he sacrificed himself to Mallus in order to allow the other Legends of Tomorrow to escape.
The Season 3 finale first aired on 9th April 2018, and we expect Season 4 (which sees John Constantine join as a full-time member of the team) to begin in the Autumn – probably in October, roughly at the same time Doctor Who Series 11 airs!