Al Hilal has signed Kalidou Koulibaly from Chelsea. Leaf fall continues at Chelsea. They will be missing all their key players. They lost stars like Kante, Koulibaly, Havertz, Kovacic. It is very difficult to replace them. What will be the new transfers, will these players be replaced? This is the main question.
When a player leaves a club due to a sale, a quality replacement is brought in right away. Players are sold and replaced before each new season during the transfer windows. That's football business for you(sold and bought better ones).
It won't be difficult for Chelsea to find a better substitute for the players you highlighted, in my opinion. If you look at Chelsea's new starting lineup, you'll see that the players you listed have already been replaced out for the matches of the upcoming season, and the new players are much better than the ones that were sold.
Possible line up for chelsea next season.

The players Chelsea have acquired, in my opinion, are intended to replace those they have already sold. However, I would advise Chelsea to think carefully before selling any players, as it will be very challenging for the team to bounce back from a poor performance if they didn't check everything out first.
We all know that Chelsea is one of the top teams that will purchase players regardless of the cost. My recommendation to Chelsea is to purchase good players rather than those who will perform this season, such as those who are not properly trained.