He's not as unrealistic as you might think. Malfurion seems to practice stoicism to one degree or another. Or at least he follows a philosophy that bears some similarities to some elements of stoicism. Some people try to avoid violence whenever possible.
Keep in mind also, that at the time of Malfurion going to sleep for so long, he was immortal and so was Tyrande. From his perspective, it's not like he was missing out on anything. I'm sure he thought they were going to make up for lost time in the trillions of eons that were to follow that.