Steps to reproduce:
1) Download and open attached project "AudioCrashTest.zip"
2) Make sure VR mode is enabled in player settings
3) Make sure Rift audio is enabled under Playback devices in your computer and Rift audio is not a primary or default device
4) Build and play the project with scene "AudioCrashTest" included
5) Once the project is playing, unplug Oculus headset USB cable (not the HDMI)
6) Wait until error appears in build (notice no audio is now playing)
7) Plug it back in
8) Exit the app

Actual result: Crash
Expected: It shut downs correctly, no crashing

Tested and reproduced on:
Windows 10
Oculus CV1
Unity 5.4.5p2, 5.6.1p1

Note: On 5.6.1p1 it crashes on simply unplugging cable

Not reproducible in:
2017.2.0a1, 2017.1b8