We cannot rule out she wants to spend quality time with her partner instead of spending time in a recording studio, so that, if the worst outcome comes, her husband can remind her of what she lost.
I'd make no presumption, good or bad, about the their relationship dynamic, however.
She can, but she might not. A lot of that depends on how he presents the idea to her -- it might seem like something that's important to him.
Honestly there is no doubt a very large emotional/personal side of this, irrespective of who's idea it is and who supports it.
Technology isn't the solution for all problems and challenges in life.
But good lord, sometimes trying to get technical help on the Internet turns into this rabbithole of people who are specifically looking for ways not to be helpful. "Did you really want that?" "Did you consider alternatives?" "What you really have is an XY problem."
#1 item from https://www.molfar.io/blog/yc-questions
Sometimes a cigar is just a cigar.
He then goes on to say "My ideal would be an open source 'deepfake toolkit' that allows me to provide pre-recorded samples of her speech and then TTS in her voice."
That sounds like wanting to capture and simulate someone's voice.
Literally the only person on this thread who knows anything about the OP's wife is the OP. Everyone else sharing an opinion on "the emotional side of this" is vocally ignorant.
And it's particularly useless when your worries are about a situation which does not concern you and which you are almost completely ignorant about.
The sentiment is admirable, but it's a lot of work considering that the probability of a negative outcome is very low.