Don't give up yet. They might come back from the roots and the protected part of the trunks. But it will take time. Several of my hardy ones always have some leaf damage when the temps drop that suddenly but they always come back.

God only knows how many camellias I've lost over the past 10yrs, but here's my advice for anyone trying to grow them below 0F. I live in Toronto, Canada and have pretty good luck now getting them through the winter.
1. Never cover them with styrofoam cones like you would with roses. I tried it before and they all died. They need some light. Styrofoam cones work only if you cut a window at the top and tape some plastic over it so sunlight gets in.
2. Sorry, but never mulch directly against the bark in truly cold climates. Root zone is okay. However, the bugs and moisture(from the snow) in the mulch can rot the trunk if in direct contact. I've seen the bark peel off like cellophane 2 yrs in a row where there was contact (until I clued in), but bark above mulch remained totally intact and healthy.
3. Wrapping is a must. They won't survive here without some protection. Also protects the buds from squirrels. The trick is to protect them before the hard freeze comes.

I also think they'll resprout from the base. I find that their hardiness improves as they get older. First winter is always tough on plants.

I think you will have better success overwintering them with using Wilt Pruf on the leaves to prevent leaf browning before the 30 degree weather comes to your area. Reapply again in mid winter on a warmer than 35 degree day the Wilt Pruf. The drying winter winds cause the browning of the leaves. I see there was an extreme temperature drop, the camellias did not get a change to acclimate. Definitely wrap them with burlap to protect them from the cold before these temp extremes get to the plant.