While it is true that player departures and expected transfers will provide issues for Napoli this season it is necessary to take into account the inherent unpredictability of transfer rumours. Since Victor Osimhen contract with Napoli is still in effect and there are no trustworthy sources to back up this rumour the report that he will be joining AC Milan looks dubious. It is important to wait to draw judgements until there are formal announcements. To maintain a competitive position in Italian League Napoli can still bolster their team with potential acquisitions and rely on their strong custodian and defenders. Even if the season may be challenging they have a chance to claim a high spot if not the first then at least the second.
Although there are rumors about Osimhen moving to Milan, I'm not sure it will happen. Even though his contract with Napoli will soon expire, Milan is unlikely to bring him in as a permanent purchase. Considering that AC Milan is currently focused on buying affordable players, they might not pursue Osimhen with a buying status (maybe if he was free agents). Of course, I would be happy if Osimhen does join Milan because he would enhance AC Milan's attacking rhythm. But for now, i don't think this rumor will come true.
I also don't think the rumors of Osimhen becoming Milan player next season will really happen considering his current deal with his club Napoli and the Napoli president saying that the player is still a player of the club Napoli even though offers has come from Saudi Arabia Which is one of the bigest deals for the player but it is not considered yet because Napoli is happy with the performance of the striker who helped them to win the league last season as the top goal scorer in SeriaA. Osimhen joining Milan is going to be a huge deal for Napoli but I think Napoli will rather sell Osihmen to another club to make money when he still has one year contract with the club than letting him join Milan as a free agent that will be of no profit for the club but rather Milan will be a stronger opposition for Napoli to play against.