Napoli basically just made sure that Atalanta doesn't win the league this season. Obviously there are so many games left, so anything could happen still, but I do not think that there will be such a drastic change that Napoli and Inter both starts to lose games or get many draws while Atalanta keeps winning, that's unlikely.
Obviously Inter could still catch up to Napoli, that chance is there, but Napoli at least looks great, while they played more games, they have enough points gap too, so that means Inter has no chance but to win those games, not even a draw would be okay. Winning this game was a huge huge step for Napoli for their league title hopes, and they did exactly what they needed, this was definitely amazing for them.
At the moment Napoli are not completely immune to replacement until inter have played their two outstanding matches. Inter has to devote to winning this two matches should put inter ahead of Napoli if they succeed in winning both games. Atlanta hasn't lost all hope yet even though the chances are getting slimmer as the league competition progresses.
Atlanta still have to fight harder till the end because we can't say for sure what will happen when we start approaching the end of the season. But at the moment the competition lies between Inter and Napoli and it will take a consistent decline in performance for Atlanta to join the race again.