Yes you are right I also think Antonio Conte is great coach who can help Napoli do well in Serie A. But it's not clear what will happen to Osimhen. Chelsea was interested in him but now they might not be. Even if they offer lot of money, Napoli might not sell him. Chelsea mainly wants to get rid of Lukaku, not trade him for Osimhen.
PSG may have a higher chance of getting Osimhen because in terms of financial capability PSG are more strong than Chelsea and sometimes what the players normally consider is the impact the club they are going will actually have on their career because no players would actually love to enter were they will not be able to showcase what they've got, though Chelsea is also good for Osimhen but I always believe that PSG is more suitable for him, unless he decided to try out the English league and see how improve it will impact on his career. However like you said Napoli may decide to extend his stay for more season because in as much as Osimhen has not been able to perform the way he normally do doesn't mean that he is no longer an assets for Napoli so perhaps let's see how goes.