If Napoli manages to reach an agreement with Chelsea for Lukaku transfer, I am also sure they have also reached another agreement regarding Osimhen transfer. For now we do not know where Osimhen will go, whether to PSG, Arsenal or Chelsea, what is clear is that the most likely is to leave Napoli. Regarding Lukaku, it seems that the Belgian striker will have no trouble adapting to Conte game plan, because they have worked together in the past, especially last season Lukaku also strengthened another Serie A club, AS Roma. Actually, this transfer is quite late, an agreement should have been reached during the pre-season tour yesterday, so that Napoli could start their campaign with a win instead of a crushing defeat.
On the other hand, with the summer transfer window almost closed, Osimhen transfer seems to be getting closer, and Napoli will most likely not hold back the Nigerian international striker departure. Meanwhile, if he does not suffer any injuries, I think Osimhen does have the talent to score many goals this season. It is likely that Osimhen will choose to move to a club that plays in the Champions League, and has a greater chance of winning trophies in the near future, in this case Chelsea seems to have a low chance of recruiting Osimhen.
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.
If no club is interested, then another option is to pair these two players, Lukaku and Osimhen because we know that PSG and Arsenal have not reached an agreement on the price offered by Napoli, according to both clubs the price set is too high and even both clubs are hesitant about the price offered or Osimhen could be Lukaku's backup player or even vice versa.
This is still just my opinion about whether it is true or not because it could happen, because both have the same individual in the game pattern but Osimhen is better than Lukaku who always makes mistakes in front of the opponent's goal, and even several times Lukaku always harms his club when important matches, and the unforgettable moment was when Lukaku blocked his teammate's header at Inter Milan during the Champions League Final last season, when Inter Milan vs Man City maybe everyone remembers that moment.