This ending is OK.
You gotta do a lot thinkings to understand the concepts behind this messy time travel Mashima plotted. The only illogical part is if the timeline has taken the path where the gate is gone, the present should reconstruct and everything will be different. Unless the present, where town is destroyed and ultear is dead, has occured as s paradox that intertwine with the new possible timeline.
But there is possibility that ultear will be revived(and I do hope so!!!) And future Lucy should be still alive, because she was alive to open the gate, so she should be alive being summoned back. As it seems than the future is peaceful, possibly Aconologia defeated, so we should expect an arc involving FT vs aconologia/zeref (final showdown?)
Let's hope Mashima improve his story telling, it's annoying to think hard reading a shonen manga just to understand the story.