I am not bought on the whole "Lich King as a weapon of the rightchesnous."
First, it's a creation of Evil, the most sickening, cunning and awfully brutal evil known to Azeroth.
Second, even if Bolvar was all good and pure in life, there's this fact that there isn't a single soul that can withstand corruption forever. There are ample signs that can lead to Bolvar's ultimate downfall to darkness: he is, well, a freaking lava-man; he will be constantly tortured, time and again by the countless trapped souls that have been gathered under the Lich King's power; although it was disputed, time and again that Ner'zhul is actually dead, I disagree... that old bastard is part of the Lich King, think "source code"; he sits atop a frozen throne... period.
Third, from what I described earlier in my post, we can find cues to what is called "recycling process." And why the heck not? The Lich King had his first go and had tested his strength and available options (and crucial mistakes). The next time his Wrath will be unleashed, he will be more ruthless, more cunning and more swift in his revenge against the mortal world. I can predict some pretty gruesome deaths under his sway... just you wait
PS: Oh and, he can ressurect Arthas as a mini boss... now that would be laughable