Inter can maintain their consistency if they succeed in retaining their team and coach. that's what actually happened to Napoli. there are players and of course changing the coach's chair has a big impact on a team's game. because they have to adapt to the playing patterns and strategies of the new coach.
Their are different things that can easily affect club performance which is changing of coach and that has been one of the reasons why so many clubs that was doing well before has been performing very poor now, so perhaps just like you said in the case of Napoli their sudden decline is also as a results of what we are saying because we all know that Napoli was a very strong team that was doing well on their other seasons but the moment they change their coach and few of their players that's the time their difficulties in inperformance started.
I also agree that if Inter Milan still work with their coach they will surely be more impressive next season because their coach has been doing a good job for them especially on this season because even the Inter Milan team management could not believe the club will go this far, so actually for them to remain consistent is only by maintaining their coach because getting another coach will surely bring down the performance of Inter Milan because it will take them a lot of time to get use to the play pattern of the new one.