It really is a crap shoot ! But when I see how much the girls enjoy being out and about - in fact they are totally mad at me if we have to leave them in for a day ! - I would never lock them up. It upsets me if we lose one but I realize that the predators are only doing what they do. I get more mad when it is a dog who should not be allowed to roam ! Having said that we do try to keep an eye out but hawks are not afraid of us it seems anyway. The other day one came and landed on the roof of the coop and we were right there !! Don't beat yourself up.
So far, we've not lost any chickens to any of the hawks, but it's probably just a matter of time if we let them free range. They are pretty good about sticking close to the edges of our vehicles, the carport, etc. rather than being out in the wide open, and I've shoo'd away hawks flying overhead many times. I've even seen them sitting on a fence post or tree branch, eye balling the coop. I always go outside and yell at them. LOL 
