it is pretty bomb proof. the black bits may in fact be dead so wait a bit then if they don't re green then trim those bits off and the live stuff will re colonise it.

Agree Dan, I have several on the rockery. They have survived the snow and cold, but, one of the plants went black in the hot sun last summer.
I gently scraped away the black, watered it as I think it had dried out a little and it soon grew back and is spreading well...

Thanks guys!!! I’d hate to lose it!