It's been four years since Anton Yelchin's death and it'll be even longer until a new movie is filmed let alone released (if one ever is), they waited that long to recast Spock with whatever his name is from STD after Leonard Nimoy passed away. There's no set time limit on how long to wait before recasting.
I could see them not recasting the role out of respect, since it was an accidental death and the actor was young, but likewise I can understand them needing to recast it if the story called for it, or just including a throwaway line about Chekov being on the Reliant and having Ilia or Kevin Riley or Saavik or David Bailey or Arex or whoever filling the empty seat.
I could see them not recasting the role out of respect, since it was an accidental death and the actor was young, but likewise I can understand them needing to recast it if the story called for it, or just including a throwaway line about Chekov being on the Reliant and having Ilia or Kevin Riley or Saavik or David Bailey or Arex or whoever filling the empty seat.