This one can be a pain because Sir Morin can't stay where he is suppose to stay. The best is to leave some units near him before you do the wizard and then check where the cross is on the mini map.. move as fast as you can there with your hero and units. While they are busy going there, click on the army you have left with Sir Morin and start defending him where-ever he goes. That is the only way that I know of to protect him and keep him alive and also doing it this way you know exactly where he is. I sure hope this helps.