Osimhen was very good last year, but I think he could not perform at such a high level in the years before that. He has a not bad performance this year, but if he goes to Chelsea next year, he will try to show all his talents because the Premier league is a big showcase. Everyone will try to walk on this stage and one of them may be Osimhen. Napoli can make a lot of money from him, but they need to find a name to replace him now.
I think problem make Napoli failed raise to the Europe League or Champion League spot because underperformed with Victor Osimhen, indeed he was absent almost one month for playing with his national team in AFCON on January last month but his goals productivities in Serie A decreasing by scoring 12 goals of 19 matches. Indeed had downgrade with performance, I think Victor Osimhen still valuable and many top premier league teams until PSG are waiting for getting him on next window transfer.
Before dropping performance in the next season, seems Napoli has chance to sell Victor Osimhen with higher values above 100 million euro and try looking other players can replace well his position next season, if Napoli want to get much money better selling Osimhen before his transfer market fees decreasing drastically depend with his performance next season.