If they make a CGI Joe Biden, it’ll be groundbreaking - the first CGI with dementia!
They'd create a digital face of Biden that's superimposed on to the head of a stand-in. With dialogue still to be added they animate Biden's mouth realistically and seamlessly, viewers would largely be unable to distinguish the difference.
A completely CGI version of the late Paul Walker is featured here in the seventh Fast and Furious movie but it's not really him.