Take the valve off (just) to make it easier to work on. Use a small saw blade, like a piece of hacksaw or a fine tooth jigsaw, and make several cuts through the PVC using care not to cut much into the valve threads. Then with a thin screw driver, you should be break out the PVC in pieces. FWIW, I make my transitions from copper to PVC in a bit easier place to work on. I also avoid PVC male threads.