After going through the Igneel vs. Acnologia chapters again, and seeing that even Igneel can't do much to the Dragon King, it's not that likely that Igneel will actually win this fight. Not to mention END is seems to be more powerful than both dragons, so if END does get revived, neither of them stand a chance. No matter what happens, poor Natsu will probably lose Igneel right after getting him back.
What could happen is right before Igneel dies in some way, he gives Natsu a vague hint (because apparently nothing can ever be completely clear) about why he disapeared on 7/7/777, what happened to the other dragons, etc. Natsu & crew go to investigate, and it turns out it has something to do with Zeref, leading up the final fight with Zeref. (Also something about Lucy's mom.)
I'm not saying this should happen, but it's a possibility. I'm just curious to see what people would think about this, or if there are any other possibilities close to this. So what do you think? Would it be a good direction for Fairy Tail to go in or not? (I would put a poll here, but I'm not quite sure how...)