If you Alt+Tab for a moment in the middle of the recording, sound disappear.

I believe enabling sound in background can mitigate this issue. As far as I'm aware there is not a real "fix" for this.

If we chunk the audio files up into pieces based on word boundaries and we can hook into an event when the game is tabbed out it should be possible to automatically pause then resume the sound very close to where it was left off.

I think a much easier approach than I originally mentioned would be to see if we can hook into when the game is tabbed out of and stop the player. When the user tabs back in they can manually press play to restart the voiceline.

It's not as nice as having a mid-voiceline resume, but its probably way easier to implement.