Hi Mark,
I have a Frederick that is about 20 years old and is still producing this year. I have seen wrinkled fruit like yours on vines that have died back, but not necessarily from under watering. I think my vine has lived this long because I don't overwater. I rarely water from late fall to early spring, then only occasionally deep water once a month during summer, I think we have similar climate being near the coast. Not sure what your soil is like, but mine is clay.
I do not prune out old vines if they are healthy, only cut back to keep size contained and any parts that are dying.
Janet