The Blues can't be mended in a season; it's more like rebuilding the club, and it'll be a long time before things return to normal for the Blues. Chelsea must be rebuilt immediately, not when these players are sold by the club. Todd Boehly and Mauricio Pochettino are required to pick up their game, and this time they will sign replacements for the club's departing players. losing Mason Mount to Manchester United and Kai Havertz to Arsenal makes minimal reason; losing both of their key players to opponents would only give their rivals an advantage when confronted with the Blues.
Mason Mount was grown in Chelsea and had some good seasons there but he is no longer in a plan of Chelsea and their coaches. It isn't a loss for Chelsea by selling Mason Mount and getting money to buy other players. Players come and go and it is very natural for Mason Mount. Players can go because of their ambition to win titles, greed to want to have better salary, conflicts with the club and coach, many reasons.
Mount already left so let's wish him the best. Euro 2024 will be hosted next year and Mason needs to play regularly to have a spot in England squad.