There is a grapevine in my backyard that is in pretty poor shape. The main trunk is split and looks horrible. But every year, this thing sends out more vines. Last year, we just let them grow along the fence as it wanted. Once it got to winter, we cut it all back. We had even gotten one bunch of grapes, but they were all shriveled looking.
I took one cutting, cut at a diagonal, and put it in water. I also plan to take another cutting to try rooting in soil.
I figure if I can get a good plant to grow, I can maybe replace the unhealthy one.