ive read articles and opinions of people who say that the nerzhul/arthas/lich king love triangle is literally dead but i did find it strangely amusing that when bolvar put the helm of domination on his voice changed just as arthas' did when he put it on.
i dont think thats the last we'll see of the lich king/bolvar but im not entirely sure itll be wow that we see him in, possibly a new warcraft rts later down the road. i would have to guess the next expansion will deal with the burning legion and while they could bring bolvar back and say that kj still has influence over him thru the helm of domination its much more likely (in my opinion) that theyll do something with illidan and demon hunters