Driving without digi card

Driving in a rest period IS driving in a rest period.
Whether your card is in or not, you are driving in a rest period.
.
It really looks that simple to me.
And movement of vehicle without a card, is recorded on the head unit so if/when checked an explanation will be looked for.
A legitimate emergency movement may be ok, but a deliberate attempt to hide an obvious illegal movement may cause a “sense of humour failure” of the authorities. They don’t like being taken for mugs.