Fair warning: this might be a long read (you've raised several great questions). Remember, these are just my opinions.

1. I feel like song covers using AI are transformative, but it still shouldn't fall under fair use, because then we'd have to attribute that fair use to the AI itself. No human impersonator made that cover. A piece of software did. Sure, the programmer designed the software, but the area of the copyright - and by extension the fair use - is music, meaning the person has to actually produce the music themselves, by singing or playing instruments themselves. Coding software does not equal playing music. So the entity making the one aspect that makes the cover transformative, i.e., the dead singer's voice, is the AI, not a human being. But AI is not eligible to engage with copyrights in any way. So it's still not fair use, and therefore a violation of copyright.

2. I don't think anyone will die if they don't hear an AI-generated cover, so this is still not too far. Songs like Breaking the Habit and Given Up have helped people deal with addiction and depression. That's where the value to society lies, not in using software to create covers of those or other songs.

3. The moral right of the creator supersedes all. As long as the original creator is attributed, legally, I can't see any problem with working on music covered under such licenses. That said, it's just creepy!

4. I reiterate, under the current legal framework, no problem, but morally, it's c r e e p y !

5. This I have no idea, or even if it's true. For instance, Slipknot has a new drummer, Eloy Casagrande, and people comment on and compare his drumming style with Jay Weinberg's all the time, and I for one consider instrumentalists just as important as vocalists.