When you say they went through the 'cane, were they standing in flood water? In nasty backed up toxic stuff as in what was flowing through the streets? Or just wet and thrown about, denuded of leaves, etc.? If the roots were sound when you repotted, they are probably okay.
You can cut roses down to just above the ground and they will regrow, in fact, people often prune them quite hard. Any of the branches you are sure are dead can be cut off, but if in doubt, leave it alone. You don't want any fungus growing on the dead stems though. I wouldn't expect any new growth for a while yet, although it could happen. Give them a few months, at least until April or May, to see if they will survive.