I also think Napoli has plan for Osimhen transfer if they sign Lukaku from Chelsea. Osimhen will probably leave Napoli and join another team like PSG Arsenal or Chelsea. Lukaku will fit in well with Conte team because they worked together before. But this transfer is taking too long and it is hurting Napoli season. Osimhen will likely leave Napoli soon and they won't stop him. If he does not get hurt Osimhen can score a lot of goals this season. He will probably choose team that plays in Champions League and has good chance of winning titles so Chelsea might not be his top choice.
Osimhen can indeed leave by looking at some good options for himself and also for his career if he is no longer happy to be at Napoli this season. However, I also hope that Napoli must be willing to complete this as soon as possible before they suffer more losses through bad results this season. Because when there is one of the good players who is no longer happy to be relied on by the team, of course it will be difficult for the Napoli team to expect better results this season, unless they have a backup of the same level at this time.