They should hire a new guy. I don't really care if James wanted otherwise.
If Bugs Bunny, Kermit the Frog, Super Mario, Mickey Mouse could all find suitable voice actors to take up the mantle after the original guy retired or passed, then I'm sure they could find another guy they can pay to do a solid Darth Vader voice.
It's just a scummy play by Disney to normalize AI "performers", as opposed to using real talent, by using a major character that people have a connection to. James isn't owed an eternity of voiceover gigs, and Disney can and should pay actual artists to make actual art.