Like I said, we didn't actually catch the possum in the act, so we are not 100% sure he was the culprit in all 3 instances... but he definitely won't be a problem now! We have no shortage of predators here unfortunately. All three of our losses occurred while our girls were free ranging unsupervised. So now our girls are confined to an enclosed run when we can't be outside to watch them & we aren't shy about removing predators if we happen to come across them.
Don't be scared to get more! It happened to us too. We bought 6 chicks from TSC... 2 turned out to be roos! We thought, hey, might be fun to hatch chicks! But they were not well behaved young gentlemen. They were far too aggressive with each other & the ladies & me & my husband , but the last straw was when one of those hormonal beasts went after one of my kids

... they made delicious soup!
So, it happens to all of us on occasion, just make the best of it... worse case scenario, you get dinner instead of breakfast!

Regarding your hawk problem, you said your enclosure is covered? If you would like some ideas of how to shire it up, you could post some pics here. There are some great people who have been responding to this thread. They might be able to give you some pointers to help shore up your run to help prevent future losses.