I think you will need a run, you don't have to use it all the time if you don't want to, but if you want to be gone for a couple of days, it does allow the birds some outside time. I don't think birds should be locked inside a coop any time.
 
Predators will come to an easy meal, depending where you are, some predators are more concentrated, and in competition for food. Chickens are easy food, and once the predators find you, it is difficult to impossible to encourage them to leave. However, locking up the girls for several days, often times will get them to move on, but not always.
 
I let mine free range, as much as possible, but I have a coop/run totally enclosed too. I really think that you will lose a LOT of chickens without it and maybe even ALL of your chickens. I have lost a lot of chickens through out the years due to predators. It is part of the risk of free ranging. Right now, I have had my girls in lock up, due to a predator situation. calling a trapper in.
 
MrsK