can you fight the lich king in WoW?

Answer 1

Yes, you can still fight the lich king in Icecrown Citadel in Cataclysm, he still drops the undead horse flying mount 'Invincible's Reins'.

Answer 2

The Lich King is the last boss of the 10/25 man raid instance Icecrown Citadel found in Icecrown in Northrend.

He is a level 80 raid boss that can still be accessed however you need to clear through the full raid to get to him, the portal to his platform is only unlocked by defeating the 3 end-wing bosses (Professor Putricide, Sindragosa and Blood Queen Lana'thel) which you can only fight by getting through Deathbringer Saurfang.

Before the Cataclysm patch was released Heroic Lich King on 25 man would drop Invincible's Reigns at 100% droprate however since the patch has been released the droprate on the mount has been reduced to below 1%.

You can still achieve the 3 different titles for killing Lich King at 85, however.

Kingslayer - Killing LK on normal on either 10 or 25 man.

Bane of the Fallen King - Killing LK on heroic in 10 man.

the Light of Dawn - Killing Heroic LK on 25 man.