Damn you all for making me think something might happen!
I wonder. What if they play the whole of Rumours straight through in a small setting which is filmed and recorded for CD/DVD? Or something like that?
That way, Mick saying "she won't tour" is not a lie, but something still is happening. My only thought is that Lindsey (and maybe John) would object on the basis that the four-piece would be undermined creatively by bringing Chris back, and audiences on the tour would expect her. Also, the pressure on them/her from the label and managers to rejoin would be immense if she did that kind of one-off thing.
My instinct is still that this is just an anomaly, but I'll be very happy if I'm wrong.