Napoli last season was relatively consistent with Spalletti, but with his departure, hopefully it won't be a season sensation for Napoli even with a new coach. Because next season it will be more difficult to win and it is possible that the chances will shrink if the competitors are able to improve well at the end of the season until the start of next season. If you can return to performing consistently, it shouldn't be difficult for Napoli to at least finish as runners-up and it is possible to win again.
Don't let things ever happen in the Premier League like Leicester city won the English league and now they are relegated. Hopefully Napoli can learn from them by not selling star players, even if they do sell them they have to get a commensurate replacement.
Now Spaletti is taking a break and Napoli have signed new coach Rudi Garcia. Its success should be appreciated, where Spalletti and the players succeeded in presenting the Scuddetto title that they had not felt in a long time. Since coaching Napoli, it took Spalletti three years to build his squad so they won the Scudetto last season. Consistently winning, they managed to top the standings until the end of the season.
For next season as you said, Napoli is likely to encounter some difficulties to defend the title. However, Degradation is unlikely to occur. Rudi Garcia just needs time and complete trust to adapt to his players, in terms of tactics and style of play. Like Spalletti who needed three years to build Napoli to a Champion, Rudi Garcia also needed time to prove it.