Napoli didn't had any injured, but Juventus didn't neither, Milan neither, some injured before world cup, but not during world cup, and Juventus is getting a lot of players back very soon. All these combined, injury will not be the reason why they win, it will just not be a reason for their loss, and that's a good thing of course but their win will come with their own merit and it looks to be quite a great thing.
I think there are two possibilities. If Napoli does not sell the players that they currently have, I think they will be alright. If anything they should bring in some players. Right now, if they sell any player from the squad, they are going to make a mistake. I feel like the only way they are going to lose is if they get greedy and try to bring in money by selling some important players.
Again I could be wrong because there is no 100% surety that they will perform better after the World Cup. But I think if they just do not sell too many players and keep the one that they have right now, they should be alright. There are a lot of offers coming for Victor Osimhen. They better not sell him otherwise, it’s gonna be a problem for them.