I am not sure if they can kill the Wights, nit yet. Would Ghost be able to chew their heads off (he was definitely having a go at the Wight in the Old Bear's room)? Will they survive without a head? There is so much unclear about them yet, I wish that the new book can finally answer. But it seems that obsidian can kill them , am I not right? And some sources say that the dragons can burn them as a whole, of course.

PS: edit: the others is one of the most interesting aspects in the story for me, can't you tell. :D

I but yes, I wasn't clear enough and edited the post!