User blog comment:Miskos3/Fairy Tail 538: When the Flame Goes Out, Review/@comment-24053170-20170603054652/@comment-4933386-20170604125113

I don't know, if they were trying to give a bigger effect (in my opinion), it would be Natsu never came back to see Lucy and that... they waited and still no sign of Natsu...

Another theory is that he is indeed fading away permanently, and he ran away just so it'd be Less sad? or maybe to see Erza to give one final message to Lucy maybe...

Last theory... What IF, Natsu ultimately sacrifice himself in this final chapters in order to save Fairy Tail... just like Rob protected Erza during her imprisonment? Just for some theme that occurred at the start of the anime.