The draw against Napoli is quite natural, especially since Inter Milan is in a slightly slumped mentality after being eliminated from UCL, but I think no one doubts Inter Milan to win the Scudetto this season, they are already very far ahead in points from their rivals and also in terms of the quality of the Inter Milan team. This season is very strong so it is not difficult for them to recover, losing a few more matches in the continuation of Serie A matches this season I think will not have a significant impact on them because it is very likely that Inter Milan will ensure the Scudetto this season.
After been eliminated from the champions league, it was actually really natural for inter Milan to have a slow moment because their psychology will definitely be affected and their minds aswell will also not be the same because they are definitely going to be affected for a while getting knocked out of the champions league, one in which last season you were able to get to the finals, it's actually disheartening.
It's affect their performance slightly but I'm sure they will pick up nos sooner and get back on track to winning ways so they will be able to maintain their position and be able to focus fully on their trophy back in the domestic league since they couldn't win the champions league, they will be able to see if they can win their own domestic league and see that as an achievement for the season rather that going trophyless this season. The champions league was actually causing some form of distraction to them because they actually did focused more on it than they have done on their domestic league.
Napoli who is the current defending champions u fortunately may not be able to completely defend the trophy this season because they ha e actually been left far behind in the league as inter Milan is already very far ahead if them in point and it will take them actually a whole lot to be able to meet up with inter Milan at the top before been able to think of winning and defending the trophy this season, rhey could go get improved and hope to win it again by next season probably but this season seems to be out of it