You better get used to it
At best, we should perhaps get used to the fact that in the future E Street Band projects will be the exception to the rule rather than the other way round. Tours... if any... will be shorter and have an air of exclusiveness to them. Unless of course Bruce chooses to find replacements for Max Weinberg and Clarence, but that seems unlikely. Instead we may see individual members of the E Street Band be part of other bands backing Bruce, but a show billed as "Bruce Springsteen & the E Street Band" with Clarence and Max missing... would that really be desirable? I don't think so. It could very quickly become embarrassing for everybody.
One of the bands that people like Danny or Garry could be part of may very well be the Seeger Sessions band. In the last few days of the tour Bruce more than inclined that we haven't seen the last of them. But the size of Seeger Sessions Band makes it inevitable that they won't be able to maintain the same lineup for probably even two tours in a row. Members will drift in and out, much like it's the case with Southside Johnny's Asbury Jukes (which pretty much only has two core members: Southside himself and Bobby Bandiera). There will be plenty of room for Bruce to ask his old E Street buddies to sit in on a few tours. And who knows, gradually we may see the Seeger Sessions Band, in various incarnations, become the new "main" band for Bruce. The recently ended tour showed that they are more than capable of playing Bruce's own songs, so even if they continue to call themselves the Seeger Sessions Band, the focus may shift toward playing more and more of Bruce's own compositions. Heck, we may even see them add electric instruments and play rock. The good thing about this band is that it's a totally flexible entity. It can do and play anything and give Bruce complete freedom, which is what he likes.
Whatever the case, Bruce in his older years is not going to slowly retire. In an interview with the press before the show in Copenhagen he said they would have to carry him off the stage in a casket. He has no plans of quitting writing music and performing, and no matter what band he chooses (and I mean, I could be completely wrong about everything I just wrote), I think it will be worth following.

