If that is the case that Victor Osimhen contract with Napoli will end after next season and this is happening then surely Napoli are really risking it here in their frustration tactics of the Osimhen to Galatasaray deal. Though the deal to Galatasaray for Osimhen has reached a very close finished line of negotiation between the two clubs but if it happens that things don't go fine with the deal then Osimhen should be patient for his contract to end and as a free agent he can pick a club if his choice to play for.
However, he shouldn't be left without a club during this period. If he does, he'll be taking a year off from football, but fortunately, the transfer window in Turkey ends later than in Europe. If he doesn't transfer to Europe, everything will be finalized during the ongoing transfer window in the Turkish league. This is a critical transfer for Galatasaray and the entire team is waiting for this transfer to be completed.
Though I don't wish him to stay without a club but if that happens he wouldn't be the first player to stay a season without club. Paul Pogba was a typical example, all that time he was having personal training, right now he plays for Monaco. While the circumstance to that of Osimhen might be different from Pogba's, the chances of Osimhen getting a club immediately is high due to his quality. All of this will be what to expect next on if the Galatasaray deal fails.