First of all, I don't think Manchester City is going to make big changes in the team. And secondly, even if some players do decide to leave Manchester City right now I don't think Manchester City is going to face too many problems. Manchester City is currently the best club in the world. So, I don't think they are going to have any problems trying to find players who will be as good as the players that they had, if not better. I do not think unless the players want to leave Manchester City, Manchester City is actually going to make any big changes.
After winning the treble this season, Manchester City may be the best team in the world. However, if they do not spend enough money on acquiring new players, the void left by the previous ones will not be filled, and they will struggle in the coming season. Those players who are about to leave the club should be known to the club by now, and planning for their replacement should be underway. Manchester City have spent a lot of money to establish such a strong team, and if they want to keep it, they'll have to spend money to bring in new players as the old ones are leaving.
I have no idea how Chelsea wanted to get back the confidence they lost, they are a great team and they have many of famous players, also Chelsea got enough money to hire the better players they want but first have to wait for Pochettino and trust him to give the list of players.
However, Pochettino made a big risk by accepting the offer he had from Chelsea.
Everything in life is risky, and the only way to discover your actual potential and win big is to take risks. Pochettino is an experienced manager, and many people anticipate a significant improvement in the team's performance by next season. I hope he does not disappoint the team or their fans, and that he makes the most use of the squad he has to bring out the best in the team.