There is no easy answer.
Yes, I liked seeing Tarkin in ROGUE ONE - but the idea that an actor, even if the legal rights to use his likeness were bought, can be used in order to appear after his death, not knowing whether he would have wanted to do this role again or do it in the way it was done for him, is troubling. Are actors really just a commodity that can and should be used how one sees fit?
If actors are alive and agree to it themselves - then it would be much easier to accept. Carrie Fisher agreed to her "cameo" in ROGUE ONE. Cushing could not.
In addition to that I think the technique still is not perfect. Simply because the unpredictability of human behaviour and gestures is what makes an appearance look human. Tarkin in ROGUE ONE still had that kind of CGI feeling, even the subtlest motions of his face reminded me of an animated character. A real actor would not have grimaced that way.
On the other hand I am scared of the day this technique really becomes perfect. Then nothing can be taken for real anymore, and no news reports can be trusted then. Sure, this technological process cannot be stopped, the invention is there and will be abused like every invention has been. But it remains a problem.
Personally, I would have been content with showing Tarkin just once, in a reflection on a windowpane, like he is introduced in ROGUE ONE. Maybe one or two sentences in a dialogue, showing a double from the distance - that would have been enough for me. And maybe it´s knowing that Cushing is not there anymore which ruins the suspension of disbelief. One rather looks at it contemplating how they did it, thereby taking one out of the story instead of immersing one.