I dunno about that....
There's a guy that deepfaked porn with:
Rose Namajunas (26:17)
Arianny Celeste (16 minutes)
Gal Gadot (multiple - 47:04, 31:05)
Melissa Benoist (SuperGirl - not sure the runtime)
Alison Brie (2:14)
Natalie Portman (multiple - 5min, 21:27, 11:47)
Elle Fanning (12:37)
Scarlett Johansson (multiple - 19:24, 5:43, 17:52)
Pink Power Ranger (12:06)
Britney Spears (mixed with a music video, so not sure the deepfake runtime)
Emma Watson (multiple - 7:46, 16:23, 20:00)
Sophie Turner (multiple - 14:34, 13:07)
Selena Gomez (11:43)
Alexandria Ocasio-Cortez (AOC) (27:31)
And he just recently did Kamala Harris (5:10)
All that done by one guy for fun, and within just the last year.
With Disney's budget, processing power/render farms (deepfakes are incredibly processor intensive), and a small pool of talented people, they could EASILY deepfake the handful of scenes a year that Luke would be in.
This list above is over 6 hours of deepfaked scenes (with pretty much constant deepfaking required, since the "actress" is shown throughout) all done by one guy. To put that into perspective, that's more runtime than an entire season of The Mandalorian. Now figure Luke would only be in a small fraction of scenes, at most it'd be <30 minutes of necessary deepfaking. That's an EASY thing for Disney to do, and certainly well within budget.
Hell, a couple years ago there were deepfakes made by people in their spare time that totaled >2TB of files. IIRC at that point it was somewhere around 500 files and a total runtime somewhere over 50 hours. And that was back when the technology was infantile, and was done by solo people using just their home computers (i.e. not render farms and not a team of people). And that's just the files that were posted to one forum.
TL/DR:
A handful of people using today's tech, and the rendering resources of a render farm (render house), it'd be very easy to deepfake Luke.