City's spine that they have relied upon for the past few years (Hart, Kompany, Yaya, Silva and Aguero) is definitely coming to the end of its lifespan.
They have had a very good innings from them, but with Kompany being more and more injury prone, Yaya just not bothering, Silva becoming less and less effective, and Aguero being far more of a home goalscorer than an away one, they will surely have to be thinking of trying to replace them sooner rather than later.
Aguero is still a top class striker, but he has said that he wants out, so they should be looking to replace him, rather than waiting until the very last moment, and panic buying.
A period of transition for Guardiola perhaps, that would be a new situation for him to come and try and do well with a team in that sort of situation.