The Napoli vs Inter match will not be a match that will elect the winner of Serie A but it could give an important clue as to who could win it.
Currently, only one point of difference is easily recoverable, assuming an Inter victory it would become 4 but it will not be a sure advantage until the end of the championship. If Napoli wins, Inter would find themselves at -2 again, and in any case it is not an insurmountable advantage.
Whoever wins tomorrow doesn't give much of a clue as to who's going win the league. There are 12 more matches to go and anything can happen. Looking at the top leagues in europe, the way the table is right now, you can easily predict who's going to win the league but the Italian seria a is the exception. The differences between the teams are not much and they've been displacing and over taking each which makes it very interesting. Inter, Napoli and Atalanta are all in the title race and maybe we're going to wait till matchday 38 for us to know who's going to be the winner.
I'm almost certain that this year we would have the winner of Serie A in the last round, Inter despite being the strongest has many commitments, and between the Italian Cup and the Champions League they will play every 3 days, Napoli instead only has the championship and can better manage their strength and hypothetical injuries. I'm only concerned about the statistics of this big match, Inter has won few direct clashes this year instead Napoli has achieved much more