I find that roses get better year on year, so I'd be very sad to have to replace them before they reach their best.
Is zone 7a too cold for them? Could you just repot them in new plastic containers? The DB suggests that most Austin roses (eg Graham Thomas, which I think is one you mentioned) are ok in zone 5 or warmer. David Austin roses must be cheaper in the US than they are here if people can replace them every year!
This winter I lost an evergreen clematis that grew in a half barrel, although it had survived for three years before that. I discovered a couple of days ago that it was a variety that needed winter protection - oops! I'll go for a hardier one to replace it.