I don't think that the owners of the City have such a deep understanding of football - for them it's just an expensive toy. They have a lot of Premier League titles, they are the most expensive players in the world and they have long wanted to win the Champions League, so once again without getting what they want, I think they can take such a drastic measure - a change of coach. There are several coaches in the world with a reputation of UCL hunter - Zidane, Ancelotti, Mourinho and a few others (probably), sooner or later they will be able to persuade one of them to take Manchester City and try to win the Champions League.
In addition, Guardiola himself may want some changes - if I remember correctly in Barcelona, he was also not so long to get bored with La Liga (and in the Bundesliga too).