Khan's Ultimate will throw Terminus away. If he has Shatterfall he can stop the momentum. He needs cc reduction 70% to do this. Instead be near a ledge before you grab him then aim diagonally down offstage to guarantee Terminus dies.
If you are at low health, using commander's grab on terminus is a really bad idea. Because Terminus is a large character, he doesnt go over Khan's head after the throw so he gets a free hit and gets closer to Khan which is what you do not want.