If they were grown on their own roots then there is always the possibility that they might recover from below surface level, rather than send up a rootstock sucker. I don't know if a rose like New Dawn will sucker. I would cut it down to about three or four inches above ground level, so that if there is any life left in the roots they may produce a new bud or two. It's an outside chance, but you never know.Just checked, and New Dawn is a VERY hardy rose:
I have the same problem with several of my roses so have fed them and watered them and given them the pep talk. So far teasing georgia, Tess of the Durbevilles and Falstaff have responed with new buds at their base. Two Benjamin Britten, two Malvern Hills, two Molyneux, one Queen of Sweden and one Geoff Hamilton seem to be goners. Some ground cover roses are dead too. New Dawn was weakened in a period of -30C three winters ago - she died at -25C the following year - and a huge Kifstgate was cut back to one single stem and has only just started getting back to a normal size.
On the bright side, Gertrude Jekyll, Constance Spry, Generous Gardener, Sceptr'd Isle and previously wussy William Shakespeare are doing well this year.
Wow, Obelixx, I knew it was cold where you are, but that's awesome.
I was sure my bay trees were goners until yesterday. Practically every leaf was brown, most had fallen off. I started cutting them back, and when I got half way down I noticed that the bark was juicy inside, but not a sign of a bud anywhere. And then I saw two little red dots an inch above ground level on one of them. So there is still hope.
My campsis radicans Indian summer looked dead, but yesterday I saw a couple of shoots at ground level.
And as for the rule that ceanothus don't break from old wood, I have one that looks dead as a doornail, but just noticed several small green shoots breaking from the main stem at the base, and it's about two inches thick.
We didn't get that cold this winter. The killer was having an initial cold spell with no insulating layer of snow followed by an unusually warm spell in February that got everything excited and was then followed by nasty hard frosts which froze them to death. Sundry shrubs are also dead and my holly hedge now has huge gaps afetr the dead stuff has been pruned out and I'm now down to one pyracantha from 5. It's almost bare apart from a few shoots just showing but is a shadow of its former self. My gunnera is dead too but the ornamental rhubarbs are looking splendid. Win some, lose some.
What seems to have happened to my sisters roses is that the snow have borken the main stems rather than they being frost damaged so there might be more hope for them than I thought.
More like 'lose some, don't lose some'. But you have to be philosphical when it comes to nature.