Napoli is also aware that when Osimhen plays another good season, there isn't really any risk involved when they decide to sell him next season. They would still make a lot of money from that transfer unless he gets injured or his performance is really bad, but I guess he will stay a solid season. It will still be about the team effort and not so much about individual performances Napoli played so well because of the team cohesion and team spirit. Otherwise you can't play more than half of the season and only lose a single game. That was an incredible team effort and that one is tough to be repeated.
If Napoli sells Osimhen for next season it is the right choice because for the 2025 season he is out of contract and of course a free transfer status that will not provide any amount of money for Napoli.
After all, by selling Osimhen in the remaining one last season Napoli can still ask for a high price and have nothing to lose on the sale, Napoli can actually buy another, younger player to replace Osimhen.
Napoli still has a large percentage for this season of getting the championship trophy.