In the end, this is basically what happens:
-Dumass is rescued from the spiders, and then ventures off to the Barrens. He spents the rest of his life trying to swim there, as he doesn't understand the concept of Zeppelins.
-Johnny Awesome's horse is killed by the Undead, and together with the player he avenges his horse. He spents the rest of his life as a guard at the mushroom farm.
-Kingslayer Orkus is the only one with a Heroic end... He discovers and finds the Stormpike Battle Plans, and sacrifices himself so that his companion (the player) can fly off with his Frost Wyrm, Kasha. Kasha however turns around and picks up Orkus, though he dies on the way to Tarren Mill. He is then declared a Hero of the Horde, as he had always wanted in life.