The good news: My rhodendrons are not, in fact, dead. They have green in their twigs and their putting forth new leafs and flowers (albeit small ones).
The bad news:
Some invasive species with an aggressive rootsystem is invading my stone walls. I thought it was called "lady bell" but Googling I can't find a mention. The stuff isn't Japanese Knotweed, thank the Lord of Your Choice. It is low to the ground and is said to bear white flowers that look a bit like lily of the valley. I've ripped most of it out, but maybe I'll post a picture of it tomorrow and someone can tell me what it is....