Sam committed a major offense against both Randyll and Dickon Tarly when he made off in the middle of the night with the family sword, and we already knew that James Faulkner was set to return as Randyll, so Freddie Stroma’s return as Dickon felt practically guaranteed.
Of course, he only appeared in one episode for a matter of minutes, but Dickon felt like somebody who would be around for at least a few more episodes in later seasons.
It seems Freddie Stroma was too busy with Time After Time to film for Game of Thrones Season 7, which gives him the bragging rights that he managed to leave the world of Westeros without his character dying a horrible death.