Brendan,
Listen to Allegra, I feel confident her suggestions give the roses their best
chance of survival..
But there is one other thing I would do: Take cuttings. There's lots of advice
on getting cuttings to root on the internet and it seems each person has
his/her own personal favorite. In addition to using which ever method your
prefer, I would also give some of the cuttings to someone else for rooting.
With roses this precious to you, you want to do everything possible to ensure
their presence in your garden.
Julie