User blog comment:Imhungry4444/Fairy Tail Wikia Podcast 10/19/13/@comment-3290324-20131023003443/@comment-24039250-20131023020723

Destroying the book would be too cheap, similar to how they destroyed the Eclipse Gate. I doubt that Hiro would do that again, since I remember hearing that he just wanted to end that arc since it was getting really long.

I feel that Tartaros will likely end with a Natsu and Igneel reunion and a team up of father and son to destroy their foe. The cost of that battle will be Igneel's life, but he will then pass his power to Natsu resulting in Natsu gaining great power, likely enough to unlock Dragon Force to its fullest. Then after everyone is crying for his loss, Zeref watching from a near distance will say that he is finally ready and that after 400 years of waiting the TRUE FINAL BATTLE will finally begin!

Tell me what you think of this theory.