Hello Geoffbca.
What I have done in such a case, I left them all as they
are now and just waited to see what would happen on these
poor plants in the coming spring.
I don't think it better to cut them off as there would be
a possibility that a young sprout would still be alive and
it would start growing when the warmer climate comes back
again.
Stan

They will probably be fine, when it warms up. The important thing is to remove any tissue which is brown and spongy, as this will spread until it consumes the whole plant. Dry, brown portions can be removed, but it is no absolutely necessary.