Leaving aside the not-inconsiderable issue that Axl teaming up with the old band would inevitably mean shitting on people who he considers friends and who've been loyal to him for a decade or more in some cases, I could sort-of see a compromise line-up working.

Fortus on rhythm (he's more reliable than Izzy, plus he can jump around on stage in a way which Slash and his pacemaker can't), Sorum or Frank on drums, Duff and Slash rounding out the band with Dizzy and Pitman on keys. That'd keep a roughly even balance between the Axl and the Slash camps. Izzy could drop in for odd gigs and have a songwriting role on the next album, and Huge could contribute songs.

That could be workable (and, crucially, could be billed as a GN'R reunion) - but as I said above, that'd mean giving DJ, Frank, Bumble and Tommy the boot. And I really couldn't see Axl doing that to his friends; why would he fuck over Tommy, who's stood by him since 1996, just to tour with someone he's described as a cancer?

No, there's no realistic option - assuming you're a ruthless businessman who wants to break up Axl's band and force him to tour with other GN'R guitarists - other than bringing back Slash. A businessman like Azoff would look at what the "general public" consider to be GN'R, and in the minds of the general public, GN'R is Axl and Slash plus some other guys.

The general public usually latches onto two members of a band as the "essential" components, the iconic members of the band. Generally, they're the singer and the lead guitarist; everyone else in the band is disposable. Mick could not tour as The Rolling Stones without Keith, Page could not go on the road claiming to be Led Zeppelin without Plant. Queen had a hell of a hard time convincing people that Paul Rogers was a worthy replacement for Freddie Mercury, but no-one other than hardcore Queen fans gave a shit about the fact that John Deacon wasn't on bass. Drummers and bassists are pretty much disposable (unless they're Flea in the Chilis); note that Page, Plant and Jones were able to get away with calling themselves Led Zeppelin, even though they had the wrong Bonham in the drum stool. There would be a fucking uproar if Liam Gallagher toured as Oasis with the members of Beady Eye, even though they're the most recent Oasis line-up minus Noel Gallagher; by the same token, were Liam and Noel to get back together with a bunch of other musicians backing them, they could quite happily call themselves Oasis.

Axl could tour with his current band, replacing any one of the guitarists with Slash, and all the naysayers, the idiot DJs slating him and his band, the watercooler gossip, would just melt away. Because GN'R is, as far as the vast majority of the record-buying public are concerned, Axl and Slash. If Axl brought Izzy in as a regular member, the hardcore fans would go mental - but the general public couldn't care less (despite the fact that Izzy was, ironically, more crucial to the original line-up than Slash). If Axl brought Buckethead back, some fans - a subset of a subset of fans - would go mad for it, but Buckethead doesn't have the iconic resonance with the general public that Slash does.

So if you were a ruthless businessperson looking to tour a "reunited" GN'R, you would want Axl and Slash up there. Duff and Izzy would be bonuses, and no-one really gives a toss who's playing the drums (sorry Matt and Steven. And Josh. And Brain. And Frank.). The trouble for those ruthless businesspeople is, Axl doesn't want to play their game.

Could someone dial down the guitars and overlay the vocals, drums, bass and piano over the Brian May version?

I like Libertad. It's not up there with Contraband, but there are some good songs on there; Let It Roll, Just Sixteen, The Last Fight, Pills, Demons, Etc...