Gundogan is certainly a key player in Manchester City's squad. He may not have scored many goals or assists, but Gundogan has been instrumental in keeping the team's overall performance stable. The important thing is that Gundogan has been with the Manchester City squad for a long time. Because of this, if Gundogan suddenly leaves the team, it will be difficult for Guardiola to fill his void. But Guardiola is an experienced coach. He may be able to find a suitable replacement for Gundogan very quickly and stabilize his squad.
At his age I think that like it or not Manchester City already have plenty of options to replace Gundogan. With the support of funds and having players above average in individual skills it is not a big problem if Pep Guardiola loses him. Gundogan has contributed a lot and now he has the right to decide. Manchester City have won maximum trophies in every competition and next season's targets will definitely continue to be expanded. Apart from Gundogan maybe Pep has been thinking about this for a long time. Clubs that want to take Gundogan will definitely have to make a bet with the condition that they are no longer young.