I have resisted the temptation to MH Ryleh for this very reason. Also, if you have an exposed asset that you are pretty sure will be mind-hunted you can try to cloud-trapeze or teleport an astral mage in there to intercept. Of course, you run the duel risks of a 50% chance that his ritual will go off before yours and the chance that your opponent will simply decided not to MH that target.