Gundogan was a key player for Manchester City. But I don't think Manchester City will face too many problems without Gundogan in the squad. Because apart from Gundogan, Guardiola has some excellent midfielders like Kevin De Bruyne, Hernandez, and Bernardo Silva. Because of this, Gundogan's absence in the midfield will not be felt much by Manchester City. Because of this, City's performance is more likely to continue in the next season as well. Guardiola has had enough time to strengthen the bond between his players. Hopefully next season we will get the opportunity to enjoy more excellent gameplay from Manchester City.
Pep Guardiola still difficult after losing İlkay Gündoğan although has replacement with Mateo Kovacic or Kalvin Phillips because both of them need adapt with Pep Guardiola games play, new recruitment Kovacic need time for adapting how to play well as holding and has function as attacking midfielder. I think Kevin De Bruyne and Bernando Silva are playing with attacking typical can manage well as holding midfielder like İlkay Gündoğan.
But losing one player its not problem for Pep Guardiola, Manchester City still dominance above 90% old squad and has chance to defend with their Primer League tittle next season.