As title says, I have both the .wav and .xmv voice files for an NPC. Used .wav to generate the lip file. I'm sure I read somewhere that after generating the lip file the .wav is no longer needed - correct?

Wave are not required for audio to work. If you pack the XWM and LIP files into a FUZ file, then technically all you need are the FUZ files. (Wave, xwm and lip can all be trashed)

However I strongly recommend you keep the wave files around locally. It makes editing the clips far easier. Down the line if you decide to change something, maybe cut a bit more off a clip, or remaster the audio (Even out its volume or bass better, etc.) it's really hard to do that if all you have are FUZ files. However, if you've kept the wave files you can just edit those, then repeat the converting/packing process to get your updated FUZ files.

I still have every single wave/xwm/lip/fuz file for Falskaar locally. (even though it's 38,000 files) I just only pack and distribute the FUZ files as that's all that's needed by the engine to function appropriately.