I agree with those saying that if City do indeed buy all the players who are alleged to be on their list, and then don't win the league, that Guardiola will get blamed for it. (Incidentally, he will get blamed in a way that Mourinho didn't after assembling the most expensive team in the history of football, but that's a digression for another time.)
But isn't Guardiola at City a different thing than Guardiola at Barca or Bayern, simply because at City he is just another shiny new toy as part of the collection of shiny new toys that have been gathered there since the day Robinho arrived, thinking he was being transferred to United? I think it lessens the man to have gone there and I'm sure part of him feels that this is far less his project than was that triumphant Barca team he brought through with 9 local academy graduates or whatever it was. That team was the opposite of the Galacticos over in Madrid, but now he has become a Galactico himself. He will realise that as a shiny new toy of the owners he is much more replaceable than he was at his previous clubs, especially Barca. "This toy is no longer shiny or new, get me a new one."
The players will know this too. As shiny new toys together, Guardiola is more their peer at Man City rather than their boss.
His task for next season is to take a bunch of toys and make a team out of them. To do so, he will have to ruffle feathers, and that's harder when he is more like the players' peer. Why should they take this treatment from a peer?
I guess what I'm saying in a roundabout way is that I won't be surprised to see Guardiola's City fail next year because football isn't just about which team is the shiniest and newest, and that includes the manager.