O.o He told you....Nice work +RepThe death of Cenarius at the hands of the orcs, demon-tainted or not, enraged the night elves, cementing their view of the savage, green-skinned (although red-skinned at that moment) creatures as their enemies. When Malfurion considered the possibility of allying with Jaina's and Thrall's forces, observing that they fought against the undead as well, Tyrande vehemently rejected the idea and cited the fact Cenarius had been killed by them as proof that they were the enemy.
Since his father Malorne was said to have a strong connection with the Emerald Dream, due to its connection to nature, Cenarius' spirit was able to live on in the Emerald Dream as a spirit of nature. The night elves believe he sleeps in the Emerald Dream while his wounds heal, and that he will some day join them again.WoWRPG 251
The only clue to Cenarius' current activities comes from a conversation his son Remulos has with the spirit of Malfurion when players complete a particular quest. It appears Cenarius is now helping Malfurion combat The Nightmare that is disrupting the Emerald Dream, causing the corruption of The Four Dragons among other things.
It is believed that he will manifest a new body and return to the world if given enough time to recover.LoM 15