Personally I think that if there is a collective will for the 5 of them to make some more music together then they'll find a way. It doesn't need to be a whole album. a few songs released on iTunes would be fine. If they all wanted to do it some of the recording could be done in L.A. and some in Kent.
The 4 who still want to tour could and Christine could sit at home and mind the dogs.
the trouble is the number of "ifs". As the great Ruud Gullitt (footballer and manager) once said "if my aunt had balls she'd be my uncle"
I do not think the collective will exists.
Once Stevie started making her "not without Chris noises" if I'd have been Christine I'd have changed my phone number in case Mick got on my case.
I think she probably feels that if they recorded together the pressure to tour would inevitably follow. She never really enjoyed touring all that much and it's been 10 years. I just don't think she can face it. I would rather she sat at home and not tour out of some missplaced sense of loyalty or duty which would show in her performance.
As she once said "it's time to put the baby to bed"
Gail