I've made the same point over and over. Maul isn't human. We don't know if being cut in half has the same effect on Zabrak as it does on Humans. For all we know, they don't have any vital organs in the lower half of their bodies. Also, a lightsaber cauterises a wound, even a bisection, so he wouldn't have bled to death, and finally he's a sith. Many sith have survived far worse, Darth Sion was practically disintegrated and held himself together using the Force alone.