Break the transfer window and also the world cup will still have an effect on the team. Even though they are not part of the national team squad that represents their country for world cup. Example the physical and mental health of the players that will change when the league returns. This is something that the teams who are fighting for the championship need to be wary of. Changes in the formation of opposing players from the transfer window can make the opposing team better. So, Napoli must be careful and maintain the physical and mental players in order to continue to appear consistent after this break.
The return of the players to their home countries to provide support at this World Cup for a while in my opinion is a natural thing and, however, it seems that Napoli doesn't have many outsiders so it won't be an important problem for Napoli and you can say they are at the moment currently taking a break to prepare for the next match of course after this World Cup is over.