User blog comment:Derax-Pagani/Chapter 507: Voice/@comment-4507125-20161024165657/@comment-7418318-20161025075714

Not to mention impossible, if you mean the GMG gate. When that gate was destroyed, everything that had come through was sent back to their own time.

But in turn that means that either the gate that Zeref used to send the Dragon Slayers into the future was different than the Eclipse Gate from the GMG... or it's still around somewhere.