Lich King will be a boss in the next patch. As of next patch, Alliance and Horde assault the Icecrown Citadel and Lich King will be the final boss. The battle will take place on a plateu where his throne is located.
Appearantly, one of his abilities is that he can shatter the ground beneath his target and have them fall into the abyss.
I just hope Blizzard had better make it an epic fight, hesw been the major boss in the minds of a lot of people, always people were talking about fighting the LK at level 100 or w/e they fantasised back when we were all leveling to 60. If they make him predictable or boring then It would be a great shame.
Actually, most Wrath of the Lich King players I've spoken to has wanted to fight him already on level 80. Only a handfew has wanted to wait for him to make an appearance.
Because World of Warcraft is lore inaccurate, most don't care which level they fight him on for as long as it's a good fight.
Level 100 is, if coming at all, a long time away and I can't imagine anyone wanting to wait that long for him. At least not if you're any fan of the Lich King.
I doubt he dies, though. According to Cataclysm, the war against the Lich King continues even at the point where Deathwing rises, and he doesn't rise until next year. You fight Lich King this year.
For this expansion, we'll be fighting Ragnaros at full power. Not his greatly weakened self that reside in Molten Core.