Slagmaw was only supposed to be on blizzcon bundle but due to a bug players opened it in packs
They did not say anything of what they do now , but for players like you i expect it gets rerolled in a different signature legendary in a future game update.
The problem will be with players who didn’t buy the blizzcon bundle , will they remove it and replace with something else ?? ( because it was supposed to be a blizzcon only reward )