I think the Screen Actors Guild would have some issues with using a CGI replacement.
They got into a very big battle over this when Crispin Glover declined to appear in Back to the Future Part II.
They hired some other actor to do an impersonation of him
in the part. It cheesed him off and now union rules
prohibit that.
Well, if TV ads can have John Wayne out and about selling Coors Beer, and Steve McQueen selling the 2005 Ford Mustang, then certainly something should be possible…
...ESPECIALLY when an actor's irresponsibility keeps them from meeting already existing contractual obligations.