I don't know the answer to your question but I would have thought that something of 7' high would be strong and sturdy enough to cope with bad temperatures.
I too planted an 8' victoria plum tree only a couple of weeks ago, however, we have not been subjected to any frost.
If it doesn't show signs of improvement this year, don't give up on it, because it just might come to life in the next year spring season.
I had a small grape vine which I planted under my cherry tree in the garden. Over out winter period we had freezing to minus 8. It looked completely dead come the following January February (this year). However, I bought a greenhouse, dug up the vine, planted it in the greenhouse and I now have about 8 small bunches of grapes on it.
Keep your fingers crossed it will survive but has just undergone a shock with the frost.