There is at least two managers in the somewhat modern era that didn't have shelf life, and remained competive at all times for most of their career. There is no reason to believe that Pep, an absolute genius isn't more like them, and less like the others.
But, if it were the case that we had a squad in prime age and the young players stopped playing for him, maybe there would be an argument to be made about switching managers not being a terrible idea. But when the reality is that half of these players are approaching the twilight of their career and the rest of them presumably haven't even entered their peak yet, I think it is pretty easy to come to the conclusion that a major surgery in the squad while sticking with what still is the greatest manager in the world is the safest thing to do.
If there is huge issues next year with a new group of players, most critically related to our playing style being inferior to the focus on pace and directness that seems to have become the norm amongst young managers these days, maybe we can talk about parting ways with the greatest manager we will ever see