Leoric's got a level 16 talent that makes his forward-arc swing heal by up to 10% of your max HP if you hit 5 enemies (including minions) with it, which works even while you're a ghost. So he spends the early game farming health globes for the level 1 talent that gives regen and then, after 16, just sits next to enemy keeps whacking away at them with an Abathur hat. He attacks a keep until he dies, gets a significant chunk of his life bar back from using the swing on minion waves that come past, respawns right next to the keep and goes again. He respawns quickly enough that the enemy team basically has to have someone babysitting the keep and the keep still goes down. Abathur has to spend a lot of time hatting Leoric, but only while he's alive.