I dunno, I think if they are to do "one final album", they should not ONLY get Christine, but also get Peter Green, Jeremy Spencer, Bob Welch, Billy Burnette & Rick Vito to also make appearances on the album. There wouldn't be any pressure on anybody to tour or have to meet expectations songwriting wise, so I would think that would appeal to Chris, Peter & Jeremy. And, because its a studio situation, those members who don't get along with other members could just come in and do an overdub or two by themselves and not have to interact with anybody else, if they didn't want to.
That would open up some great combinations of former members that we never got to hear before. Like Rick & Peter playing on a song "together"; a Welch/Buckingham collaboration (if they were so inclined); Billy, Lindsey & Jeremy together on an old '50's sounding tune, etc. It would be a WHOLE LOT more interesting (to me, anyway) than another album filled with just Lindsey & Stevie's tunes.