Pep Guardiola is a coach who is a genius at making decisions so he is already thinking quickly about what steps to make after releasing players in this transfer window. I agree with you that the team will not always use the services of old players so that regeneration is carried out gradually to balance the team's strengths in each season.
Mahrez already an aging player at 32 years old and Pep Guardiola will be looking for younger players in this transfer window. The strength of the Manchester City squad is still quite strong despite the changes that have occurred in their squad. We will see what the transfer market will be carried out by Pep Guardiola to find the right replacement after Mahrez leaves. Mahrez has found his best form after he joined Manchester city from Leicester city where he has won many trophies and ucl trophies. So he will decide to leave the European stage by joining Al Ahli next season.
Manchester City has many option for attacking line and losing Riyad Mahrez its not big problem exactly for Pep Guardiola, impressive performance from Jack Grealish and Phil Foden last season can fill position leaving by Riyad Mahrez. Pep Guardiola make their squad more competitive between main and substitute for balancing if some players leave. Right winger as position leave by Riyad Mahrez can fill by Bernando Silva and move Julian Alvarez as winger and I think its not problem for Pep Guardiola have to sell Mahrez to Al Ahli.
Since joined with Manchester City season 2018/19, Riyad Mahrez have won many tittles from Primer League, FA Cup and last tittles is Champion League. I think Mahrez have won all tittles and seems enough stay with Primer League teams looking for new challenge with highest salary payment from Al Ahli.