You can capture a Face Mask and other applied Face effects in a Face Inset by changing the Source Texture property on the Face Inset Effect to the output texture of your Scene's Camera.

To set that up:

1. Create a Face Mask.
2. Create a Face Inset. Make sure it's positioned in the Objects Panel so that it renders on top of the Face Mask.
   3. Select the Face Inset Object.
3. Select the Face Inset Component's Source Texture property in the Inspector Panel
4. Select the texture named Camera Output in the selection popup. This texture is the output of your scene's Camera.
5. You will now see the Face Mask applied to your Face Inset!