Board Thread:Spoilers!/@comment-2153169-20180221005515/@comment-34657163-20180227201241

Whether that means we’ll see other original cast members remains to be seen. “Once is home to everyone, so there’s an open invitation to every actor who has been on the show to come back in the finale,” Kitsis says. “'''We’ll see who’s available. But throughout the year, we’re going to see some familiar faces as well'''.”

I think this totally hints that gathering of those actors was more than just a farewell.