User blog comment:FairyRaven/Fairy Tail Chapter 337: The Golden Plains, Review and Commentary/@comment-60.53.102.237-20130703114213

Rereading 336 has its worth after all.

"Should the Gate ever be destroyed in this time, the existence of I, in the future should also ceased to exist as a result of the chain reaction effect." (Yukino reading from Future Lucy diary)

"In other words if the gate is destroyed now, we can alter the future to one that is bound to that one event." (Lucy's explanation on the above theory)

In other words, Mashima basically eradicated Future Lucy's timeline from existence making the events in Future Lucy's future a non-existing one.