"There must always be an Illidan" - who else is going to soak all that angst?
Solution:
Illidan refuses Xe'ra's manipulation to become The Archangel™, blasts her to pieces; then goes to a sacrifice himself to become Sargeras' prison for all eternity. There is much mourning and gnashing of teeth between infrequent cheers of joy. Back on now-sort-of-safe Azeroth Tyrande and Malfurion announce they're finally catching up with the Horde's birthrate and expect a child. Child is born with Illidan's purified soul and speed-grows up to rock the planet with Med'an. Also retains all memories from former life.
Angst-level restored!