M4A4 | Howl is fucking trash. All the M4A4/1 skins are bad.
Honestly, nothing's going to happen. The guys over at Sega did this exact same thing; they took shit from DeviantArt (yes, that's the original source for the gun as well) without permission. All that'll be issued is an apology, and maybe some money. Because they submitted the graphic to DA, they technically don't have rights to it. Go look at their ToS, it's really fucked up.