He is the only natural right winger in the squad right now so Manchester City will need to find a replacement for him in case he insists on leaving. Al Ahli are preparing an offer of 30 million pounds to Manchester City. I have no doubt his salary offer would be really attracting to the player.
The Algerian international is really a good player and for him to leave City is something Pep Guardiola would have to look into by getting a replacement but I don't see City missing Mahrez if he decides to leave because Manchester City is not a team that depends on one player, they always have players that can fit in in all positions so if he decides to leave it won't be a problem.
I wish he could stay put in England other than the Saudi Arabia league despite his age, he still have so much to give other than going for money and then retiring, such players are really hard to find.