Originally Posted by Stephen Warren
The /dev audio device files are related to the kernel ALSA driver, not the NVIDIA graphics driver. Depending on your distro, the files may physically be created by udev or similar. While there are some interactions between the ALSA driver and the NVIDIA graphics driver (e.g. to pass EDID information from the monitor to the audio driver), none of those interactions should be able to cause /dev files not to be crated, since they happen long after the device files would be created.
Audio magically reappeared. I use the Ubuntu package version to install the NVIDIA driver, dpkg does a good job of replacing old driver with the new one, however I don't know if it does anything to modprobe order. Based on what you wrote here, it sounds like a mod load ordering issue, if EDID and other information related to HDMI audio has to be validated by the NVidia driver, then NVidia driver should be loaded before ALSA driver. I am sure this dependency is hard to establish on both sides, because they are isolated projects.