In general, not so many Napoli players are in the world cup, so the potential for Napoli to continue to win in the second half of the season is clearly very wide open because Napoli can still formulate their best strategy to win games in the second half of the season. And also Napoli can improve their performances in the Champions League because the Napoli coach knows how the condition of their players is at the moment and also sees the opposing team's consistency starting to decline.
It is an advantage for Napoli if most of the players don't join the world cup, the players can get enough time to take a rest before the next matches begin. By having the rest time, it is expected that Napoli players will have a good condition when they face the next match. However, Napoli must be careful about the opportunity for some players to leave the club in January. The players may not join the world cup, but they may be busy considering some offers from big clubs. Napoli key players may be targetted by top clubs, especially the top players like Victor Osimhen, Kvaratskhelia, or Zielinski.Big advantage in my opinion. Not only they will be fresh but also they will have more time to prepare and improve whatever they need to improve during this break even if I think they are solid in all areas. I don't think Napoli will cease any of those players until next summer and if they will win Serie A , I think they will sell none of them until they have the UCL run after winning Serie A. However, I'm sure a lot of important and respectable clubs are already watching they "brains" of Napoli from the pitch.
