Hi,
I know of two ways to save that valve. The easiest and most economical is to buy a "pipe extender." (Sellers can be found on Google if you search "pvc pipe extender") With this, you cut flush to the valve and glue this fitting inside the stub that remains. It flares out and then accepts a new 2" pipe. The downside is that it restricts the flow by more than you might think...about 30%; not good but not any worse than all the pools out there built with 1.5" plumbing. The other method is to hire a plumber that owns a "Pipe Hog." This tool goes on a drill and reams out the pvc pipe stub inside the valve. I've never tried, but maybe you can rent one. Good luck with your project and take some comfort in knowing that it's a common problem.