I think it would have been a fine idea to keep Al & Dave on board, even in Mike's trimmed-down outfit, and include Brian for select larger shows. Or at least keep an open invite to the guys for any show they want to play. I remember seeing that early 2011 Reagan tribute show that Al appeared on and thinking his presence really changed the vibe ... he gave an air of authenticity. I think having Al and/or Dave would be helpful for the "brand" and probably sell more tickets and medium to small venues. I think there are plenty of fans (such as myself) who would attend a show if Al were there, but would not otherwise.
I think it is run like many businesses today. Take an airline. Cut the service to the bone and providing the flights are full and the fare is covering the costs plus a percentage as profit, why change? The pre tour blurb in each city makes no secret that Mike is the sole original. Even when Bruce had a few months off with his heart scare it was business as usual. Like an airline the only time to react is if seats are going unsold. That is not happening.