Well, they reached that point in 1993/1994. Cover Songs are a Part of their Identity. From the very first (Sweet Emotion with Tracii) to the most recent.
They did the same with Brian May's guitar solo on Catcher before they deleted it.
It could be the three of them. Dizzy and Pitman on synths and Mel does all the additional programming.
Vocals - Axl
Guitars - Slash & Richard
Bass - Duff
Keys - Dizzy & Chris
Drums - Brain
I don't think that Mel will be on any of the CD leftovers. I mean, they left Pitman's synths on Absurd as well.