There's no rot mate, just a normal transition after the greatest period in club history: the Treble and 4 in a row.
Some of the players are a bit oldish now and are being replaced by young players. These need time. Rebuilding goes together with inconsistency.
How long will it take? Nobody can say. Guess we want to compete for the trophies, but the main objective is to build a third great City team, after the 1st one with Aguero, David, Ferna, Kompany, Sane, Sterling..., and the 2nd one built around Kevin, Gundo, Bernie, Ederson and Stones.
If Pep can't win a CL place for next season, he's likely to go. Nobody is going to fire him. Given what he has given to the club, staying with us for so many years and winning so many trophies in difficult times (uefa, 115...), the club will be absolutely patient and rightly so. United were patient with Ferguson when he was failing between 2003 and 2006, we'll support Pep to the end.