[Taqwus]

Nah. They'll just use extra gems + Communion + reinvig.

They won't voluntarily exceed 200 fatigue... for themselves. The unit AI hasn't cared about communicants, ever, IIRC, but at least this can be somewhat ameliorated by a Master casting Summon Earthpower, and an Earth blessing for any sacred communion slaves. Relief also works although it's no longer the mass-fatigue-reduction one-off.