The Draenei and the Protoss from Starcraft often feel similar to one another. Both are blue-skinned creatures with elongated animal-feet (no, your dog's knee does not bend backwards. That's his ankle.) They both hail from super-advanced species who lost their homeland to an insidious threat.
One bit of Protoss DNA that was introduced to the Draenei in Warlords of Draenor was the idea of the Vigilant. In Starcraft, heroes of the Protoss who are gravely injured in battle can be put into mechanized units like Dragoons or Stalkers so that they can continue to fight after essentially dying on the battlefield. Vigilants seem to use the same principle. They can be found all around Draenei settlements on Draenor. We fight Vigilant Kaathar in Auchindoun, who is tricked by the Sargerei into thinking that we're the bad guys invading the temple. Later, in Hellfire Citadel, Socrethar's forces use corrupted Vigilants, and Socrethar himself uses one of these machines to fight us (and we use it against him.)
While it was an honorable death that did kind of pay off his story, I can't be alone in feeling like it would have been nice to have had more of Maraad in Warlords. For one thing, he was the only major Draenei character (maybe even the only one period) who came from our universe. Great though it was to get all that Draenei lore, it would have been nice to acknowledge the differences between our playable faction, who witnessed their near-extermination at the hand of the Horde, and those who were threatened with, but ultimately delivered form that fate.
We eventually find that Maraad's spirit has been laid to rest in Auchindoun (it's a little frustrating to me that we never double-checked to make sure Teron'gor was really dead.)
But it seems to me really odd that they set up this whole thing with Vigilants and then killed off a major Draenei character - this was the guy in the original Burning Crusade cinematic - without using that plot device to have him come aid us in the final battle.
There's still a possibility that they could bring him back, but that depends on how much they're willing to refer to Draenor B and its alternate timeline. Obviously, Gul'dan's going to be a major part of Legion's first raid tier, so it's not like they're sweeping the expansion under the rug.
I don't expect it any time soon, but I hold out a bit of hope for the eventual arrival of Vigilant Maraad.