As much as I do like Brain, I have to admit, I would be really sad if this turned out to be the end of the road for Guns' and Frank..
Since Brain took this tour off to be with his newborn child, maybe he'll wanna take more time off indefinately, allowing Frank to maintain his position amongst Guns'.
In anycase, perhaps Brain could become Frank's understudy, until Frank has a kid or needs a rest from life on the road
The master becomes the mentor, and the mentor becomes the master..