After thinking about this (Neil in Fleetwood) for a couple of weeks now I feel pretty strong that he made the wrong decision. Ticket sales do not look good and if you read Fleetwood's facebook page and other areas where their fans are commenting, they are pretty irate that Lindsey is not in the band and is essentially being replaced by two other singer/players....basically saying that this will not be Fleetwood Mac without him and a fake version (etc, in stronger words than that). So, in short, I feel sorry for Neil that he is in this position, especially at this point in his career. He deserves better than what will be half sold concert venues and getting some of the negative Fleetwood Mac fan comments. The good part is that he will be great vocally/guitar wise but unfortunately can't blow them away with his own material.
The ticket sales will be fine. Many of the venues (interestingly in the south) are almost sold out. Some folks are clearly waiting to see how the tour goes before buying tickets but that's expected when the main creative force in the band is fired. I hope Neil and the band record a few new songs for an EP to release before the tour as that could help a lot.