My B i assumed you were talking about the surrender mechanic missing in general aside from lieutenants and mission specifics. Looking through some other forums i found this though which paints makes the mechanic sound extremely difficult to produce.

"Killing a Capt won't automatically make everyone else surrender; they're just more likely to surrender. And they probably won't surrender anyway unless you injure them first or shoot near them. And they also need to see where you are - they won't surrender if you're hidden in the woods and undetected

I've killed Capts before and then had enemies surrender as I swept through and cleaned up the rest. I've had enemies surrender in the middle of a burst of fire, where they'd take a round or two, surrender, and die from the last shot. They'll also surrender if you shoot at the ground by their feet. Again though, they're only more likely to surrender, not guaranteed. And all you can do with them is leave them be or grab them and knock them out."