Yes, Napoli can continue to do well, they have acquired important players who can really make the difference, the fact of having such strong players means that Napoli can have an excellent championship, but there are teams like Milan who can really rise from the ashes this year so watch out for them.
Milan can certainly bounce back from this slump next season if they truly have the extraordinary ability to do so, but I don't think Milan will immediately become title contenders next season because several other teams are still very strong, especially Napoli, Inter, and possibly Roma and Juventus. So, Napoli does have the potential to continue competing for the title next season as long as they maintain their good form and avoid making any mistakes that could be fatal.