Pep Guardiola is just protecting the future of the club, he is not a kind of coach that built for just two or three seasons their in charge. Pep Guardiola wants to bring in Young stars that is why he will not allow Manchester city to give Gundogan a two years contract, if he don't accept the one year, Pep Guardiola will open the door for him to exit. Gundogan has won everything for the club and captain,he has proven to be world class, every team will buy him, because his price has increased in the market after the champions league and the treble they won this year.
Manchester city has Gundogan replacement in the team already so he won't be a problem to pep Guardiola if he leaves.
He is a firm coach who can read the direction of progress for the team in the next season so that when he makes a decision, of course he has thought about things from the start. Well, indeed the offer submitted by Manchester City, which was only for 1 season, made Gundogan not too interested in signing a new proposal which made him included in the list of players whose contracts had ended as announced recently. So, I think that with the quality that Gundogan has, he will receive offers from many big clubs for his next career. For now i think barcelona is ahead to get gundogan. But secretly arsenal also has an interest in Gundogan.
For Pep Guardiola, he has a lot of players in stock for that position. I think Gundogan's departure will not be a burden for him. But every effort is still being made by pep guardiola to persuade Gundogan to stay with manchester city.