Pep Guardiola has shown in the past that he's very good in replacing members of his squad immediately they leave his club and he does it so efficiently that the player's absence wouldn't be felt no matter how important he was to the team's progress. He did it after the departure of Vincent Kompany, Yaya Toure, Sergio Aguero, and David Silva .
However I think IIkay Gundogan still has a lot in the tank to give out when it comes to delivering top performances for ManCity but time will tell if he'll remain in the club to do more for them or be allowed to leave
Guardiola also has a very good understanding of whom to let go and whom to keep in the team. He has an idea in mind of the type of soccer he wants to play and the type of players he needs both in basic quality, but also in intensity and motivation and persistence. A good example was when he let Sané go to Bayern Munich. Sané was a strong player, but only 30% of the time during a season and we can see that again now at Bayern Munich where Sané sucks really hard most of the time. That is why Guardiola had no issues to let him go. Guardiola needs players who are willing to go the full distance and beyond, who are ready every single game of the season and who are willing to accept pain in exchange for success. Today he has a team that exactly fulfills these requirements. Manchester City can go a very high level for a very long time and just for a weekend.