I personally also thought so and indeed if several good Girona players in the 2023-2024 season are sold then it will automatically make Girona's performance decline and of course Girona will find it difficult and their performance will decline.
It's difficult to predict next season, but I hope they can still compete. I read rumors in local media that Girona are trying to strengthen the team by bringing in new players. Like Van de Beek and Gabriel Misehouy. Misehouy is a striker who can play as an attacking midfielder, midfielder, central midfielder, or even as a winger. As for Van de Beek, we know he is an experienced midfielder. Girona seems to be eager to have a lot of experienced players thrown away. This is the situation done by Michel this season.
What Girona is doing now is trying to use the money from sales to buy slightly better players. But regarding quality it is difficult to predict with certainty, because if you look at the statistics of Van de Beek and Gabriel Misehouy there is nothing surprising. In Michel hands it might be a little different and I still have hope that Girona will stay on track.