I don't think it's going to come anywhere close to the FTW shows. However, it seems like Bob has gotten his sh*t together over the last year. Hopefully, that will hold up. I don't know much about Mayer other than (as you said) he's supposedly a really good blues guitarist. I predict he holds his own, but I'm not really expecting anything magical to come out of this. I think anyone expecting Chicago Part 2 is going to be disappointed. I just expect it to be a fun time with some good music. The excitement is back in Deadheadland. That goes a long way in making a good time out of this.
Chicago was over-the-top fantastic. From here on out, everything else is just a bonus.