Even if Emma doesn’t give away what happened to Neal in the future, I predict she’ll at least tell Past Rumple about Zelena. Future Rumple’s threat about killing Zelena in the past will be actualized. And don’t forget the prophesy from Glinda’s Book of Records. Someone will travel to Oz in a cyclone and defeat the ultimate evil (i.e. Zelena). Dorothy wasn’t the one the prophesy predicted, since Zelena faked her own death when Dorothy threw a bucket of water on her. Zelena is still in Oz somewhere plotting her evil plans. I think Emma will go to Oz from the EF via a tornado and defeat Past Zelena once and for all. Zelena dying in the past ensures Baelfire lives in the future since Zelena wouldn’t have been there to lead him astray at the vault of the Dark One.
"That’s how you know you’ve really got a home. When you leave it, there’s this feeling that you can’t shake. You just miss it." Neal Cassidy