The render loop and windows message loop run on separate threads. The way the program exits is that after PostQuitMessage is called in WM_DESTROY the message loop thread signals the render loop thread to exit. As far as I can tell before the render loop thread can even process the signal it tries SwapBuffers and that fails.
My question, is there something about how Windows processes WM_DESTROY and WM_QUIT, in maybe DefWindowProc that causes various objects associated with rendering to go away even though I haven't explicitly deleted anything? And that would explain why the rendering thread is making bad calls at exit?