I believe FT will involve TIME travel. Ultear can control time.
So lets supposedly assume that the bad people mange to open the gate and dark times come. As said by ultear, if that were to happen, she can go back in time and fix everything, thats why she committed horrible crimes because she thought she would fix them anyways.
Since in future she can control time, i think she and several other survivors plan to save the past. One of the other survivors can be Levy and Lucy or even Erza. As seen around the end of manga, levy is crying with scars on her forehead writting about how all the people died.
The MY dear may refer to gajeel, since its future, they could have developed that sort of relation.
Ultear may have sent lucy/Erza back in time to save the world, Jellal came upon the future Erza/Lucy and was totally shocked, refering to the fact
"no way!"
i think that explains y levy sudddenly had scar and was cryingg when a moment before she was sittingg with lucy and celebrating.