If Napoli doesn't act fast and allow Osimhen go to the club of his choice, they'll become the loser when his contract expires. I feel that Napoli management is not looking it from this angle because they feel they have the power to dictate for Osimhen which club to go to. Osimhen does not give a fuck about all these and he didn't allow that to affect his performance.
Osimhen's contract with Napoli ends in the summer of 2026, and right now it makes no sense for them to loan him out for another year because in a year he will become a free agent and Napoli will get nothing for him. So if I were them, I wouldn’t cancel the deal with Galatasaray, especially since they have already agreed on almost everything. It's better to make some compromises on the payment terms now than to let Osimhen leave as a free agent next year.