Of 8 young apple trees, 3 appear to be dead, 3 have significant damage but appear to be acting normally (leafing out), 2 look okay.

For the 3 with damage (very significant chewing but not the full circumference)- can they survive? Or do we need to pull them and start over?

I pulled my trees, but the bark was gone a foot and a half up and all the way around. My neighbor had two trees chewed on all the way around, but only three inches up. He painted them with a latex paint, and they are budding out like normal. I have seen my dad do the same, with some success when the chewing wasn't too drastic. If they are only chewed partway around I would leave it and let the tree heal itself like a pruned branch would, though it will likely be set back some. Whatever you do they will make it or they wont, and you have a year to decide what to do.

Its really a chance, but it is hard to cut down a living apple tree you have already time, money, and hopes invested in. On the other hand, establishing a healthier tree may well be the way to go, and less angst over time.

I have a huge wolf river tree that was backed over by a bulldozer, run over by a tractor, browsed back by deer and battled shade its whole life. It is the healthiest tree in my orchard (though a little misshapen) Trees want to survive! Good luck!

One other question - on 2 of them the damage is 6 inches above the graft- should I lop off the whole tree just below the damage (there are already new shoots forming in that space)?