Ronster said:

The difficulty with getting a stand in for Peter Cushing would be the cheek bones.

Perhaps a couple of green screen Cheek Pads down to the chin would do it.

I think once you have the cheek bones and narrow gaunt chin you have Tarkin / Peter Cushing obviously with the hair do also. Crooked nose prosthetic and so on.

This model re-creation is also pretty real looking...

http://www.kotaku.com.au/2011/05/you-will-not-believe-these-star-wars-pictures-are-real/

So even if they did do a cgi re-creation they could scan that as a reference so It could possibly be up there with the likes of the schwarzenegger T-800 (terminator 1 model) which was done from scanning a cast that they used to make his fake head where he gouges his eye out.

Personally all CGI is no good though it should be a mix of both real and CGI if they go for a re-creation. especially the eyes are lifeless, so it works for Terminator but not if someone has lines to deliver.

After seeing 'Skinny Steve Rogers' in Captain America and 'Young Michael Douglas' in Ant-Man, I have no doubt they can bring back Peter Cushing. As as long as his family were ok with it, and assuming he didn't hate Star Wars like Alec Guinness, I think I'm ok with it too.