What is certain is that in this case the departure of Spalletti will have a slight impact on Napoli's overall performance because indeed we might be able to get an example when Zidane left Madrid and decided to take a break until an unspecified time. Real Madrid's performance, consciously or not, was affected by further adjustments as well as for Napoli, who indeed Spalletti decided the same thing as Zidane did.
It's a shame actually but it was an absolute decision from Spalletti.
I would not consider Napoli's condition to be the same as Real Madrid's when Zidane left, because Real Madrid could still get the title when Zidane left. But for Napoli it is still uncertain because there are still two possibilities that could happen to Napoli next season. Apart from that, the influence of the players can also be a basic reference even though the polish of an experienced coach is also very much needed by the team to make the team stronger in every season.