User blog comment:ILuvAnime/Fairy Tail continue after episode 175/@comment-211.28.37.234-20140103072346/@comment-7418318-20140103101900

To those who only watch the anime: SPOILER WARNING!

Since you mentioned the gate already being opened, it's clear your a manga reader. On the 2nd to last page of chapter 337, when F-Lucy goes to the golden plains after dying (and returning to her own timeline), we see many people there in silhouette. One of those silhouettes matches perfectly with Gajeel's rather characteristic hairstyle and is standing behind an Exceed, so it's extremely likely that Gajeel really did die in F-Lucy's and F-Levy's timeline where the letter was written, even though it wasn't fully confirmed.