As for any ethical issue, Cushing’s estate gave it’s blessing.
OK, so there is no legal issue. But I am not sure that an estate’s blessing is enough to eliminate any ethical issue.
I think this is important because Peter Cushing definitely did not agree to star in a film made decades after his death, regardless of however much money his estate was given. I also am curious how you all would feel when and if they do CGI Mark Hamill, Carrie Fisher, Harrison Ford, Alec Guinness, and whoever else they want to recreate. I think it sets a very creepy precedent.