If a run of barren years occur, I hope that Kraft would show some sentimentality to BB and not force him out, because of his faith and trust in the coach. Sometimes it would be nice if BB showed some of the same loyalty to some of the players...
I guess this all depends on how we define "barren years." The Cowboys went 13 seasons between Staubach's last and Aikman's first SB appearances and now haven't been back in 13 years again; the Niners haven't been back in 14 years and the Redskins in 17. The Packers went 28 years between Lombardi's last and Holmgren's first appearances and now haven't been back in 11 years. The Steelers went 15 years between Noll's last and Cowher's first SB appearances and then waited another nine years for Cowher's second appearance, for 24 years between wins.
I pick these franchises because they are among the storied franchises of the NFL, a club that the Patriots want to join and, IMHO, will eventually join.
I think what the Patriots are trying to do is avoid those kinds of droughts (though, in each case above there are different reasons, including dysfunctional ownerships in the 49ers case and perhaps excessive loyalty to Cowher and players like Kordell by the Rooney's).
I think it's also important to remember that the Krafts' stated objective for the Patriots is to be "competitive" for a championship every year; it is explicitly not to win the championship every year (so, a "barren" year for the Pats would be a year when they didn't make the Playoffs and win at least one game there, not when they didn't win the SB). I think they've concluded, rightly so, that there are far too many variables that come into play when it comes to winning the SB (like first game injuries to your Franchise player and magic helmet catches in the SB itself), to make the latter the objective. Whatever they might say to the public, I could see Kraft and Belichick closing the door in any August and admitting to each other "it's probably not going to happen this year, so this is what we should be doing so it can happen in two or three years."
And, to your opening comment, I do think that if, after discussion, Kraft concluded that BB had allowed the barren years to be worse than they had to be, I think he'd let him go.