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.
That is indeed the target they want to do this season, but because the value requested by Napoli is too high, several teams that approached Osimhen have canceled their intentions because they think the expectations of the form of the game do not match the price. Osimhen seems to have lost the club and he has always had problems before, from injuries to disputes with the coach. In general, this can also affect his career because if he is not played, it will make his skills not visible to other clubs.
Next season there will not necessarily be a team that dares to offer an expensive transfer value because other quality players will be born so that he will be forgotten. Napoli need to lower their asking price if they are to make that target a reality so they can use the money to make Lukaku's move permanent.