Let's say... Yul Brynner in a Pirates of the Caribbean film - I think he would look cool like a Pirate King or something. Also... let's put Charlton Heston in a Jurassic World film - I think he would be a classical type of hero, a badass man's man with little personality, but an iron determination. And he would punch dinosaurs in the face.
Let's put it that way: while I'm not against recreating actors via CGI I don't see the point in doing so most of the time, if projects like that do have my curiosity. It was done way before CGI, to be honest and most of the time it was simply exploitation, like in laughable case of Game of Death (1978).
I say most of the time, because some cases when actors died with an unfinished film and yet were preserved in the movie with all the tricks in the box turned out to be great movies. Examples include The Crow (1994). I am also very opened to possibility of finishing some of the more famous unfinished movies that way.