Manchester city is in an unstable condition in this transfer window because they have to make a big effort in keeping their players from leaving in this transfer window. Previously, two of their core players had been recruited by other teams in this transfer window, such as Gundogan who was recruited by Barcelona and Mahrez who was bought by Al Ahli. So recently, news has emerged that Bernardo Silva has started to be linked with a number of big teams in Europe and that Kyle Walker has also been eyed by a big Bundesliga team.
You're right, some concerns arose after Ilkay Gundogan and Riyad Mahrez left for Barcelona and Al-Ahli in the transfer market. Kyle Walker also has the potential to leave Manchester City for Bayern Munich which he said the defender really asked for, but the final decision is yet to be made so things can still change.
On Bernardo Silva, Manchester City have no intention of selling him even though PSG, Barcelona and the Arab Pro League team are interested in him. Bernardo Silva is still difficult to replace by another midfielder even though in principle it is always possible, but not at the moment where Manchester City has also lost two midfielders.
I think Manchester city should be able to hold Bernardo Silva and Kyle Walker for next season because they had a big influence on Manchester City game last season. So Pep Guardiola has to watch out for that if he doesn't want to lose a lot of their star players in this season's transfer window.
Kyle Walker is also in a similar situation despite Bayern Munich showing interest. Bayern Munich may be more focused on signing strikers instead of defenders, that is their need at the moment rather than defenders. But I'm sure Pep Guardiola won't be keeping Walker much longer if he wants to leave for a new challenge, but then again maybe not this season.