Since we are in the Sixth part of Tartarus Arc, I will make my thoughts on the Arc Parts known.
I believe that there are a total of 9 sections in this arc, many people think that there are 7 parts but I would have to disagree with their ideas. The reason for this because there is a Prologue part to this, so there is a part 6, I think there will be an Epilogue part to the Arc as well.
This is how I think it goes; Prologue, Parts 1-7, Epilogue.
Now as how I think the Rest of the Arc will go based on my theory.
Tartarus Arc Part Six: Magna Carta - In this part is will be what the world will be like after the activation of Face. Everyone will struggle to survive Tartarus as they now begin their attempt to revive E.N.D.. Mard Geer will show his true power and try to wipe out Fairy Tail. Makarov Dreyar returns with Lumen Historie, it will be used to restore Magic but at the cost of his own life, however it cannot reach across the world. But with the help of Wendy's efforts and Warren Rocko's Telepathy, they manage to spread word to the rest of the world and get Lumen Histoire to them (I know this maybe hard to understand but Hiro might do something so illogical like this LOL). Even though Magic returns it did not stop the Process of E.N.D.'s revival. Natsu is having a hard time with Mard Geer and couldn't stop the revival. But then Gildarts Appears to take on Mard Geer thus giving Natsu the chance to stop E.N.D.. After a long fight, Gildarts won and Natsu seemingly stop the revival but it was too late, E.N.D. is revived.
Tartarus Arc Part Seven: ???(Don't have a title for this) - As E.N.D. is revived, things took a turn for the worse as he turned his attention towards Igneel and then attacks and kills him. This in turn causes Natsu to fall into a state of despair and sadness. As E.N.D. went up to Acnologia, he convinced him to live to fight another day. As E.N.D. returns to fight Fairy Tail he was confronted by Gray, they fight for a bit but it is proven that even with his father's Magic, it was still not enough. And then, Natsu hears Igneel's voice in spirit, getting him to come out of his depressed state and fight E.N.D. and with a little help from father with Dragon Force. After a long and chaotic battle, E.N.D. was defeated.
Tartarus Arc Epilogue - After Tartarus is defeated they returned to Magnolia Town to do repair and lay Makarov down to rest. They then Celebrate their victory, we get romantic moments with couples (except for Erza, Mwahahahaha), and everyone lived Happily ever after. But then it was revealed that Natsu is possessed by E.N.D..