Once you have an initial driver rating, it stays valid for up to a year without a new trip.
If your driver rating has changed after a day where you haven't driven, it's usually because the data from your trips has taken a little bit longer to reach us, not because of the gap in driving.
You don't need to drive regularly to keep your rating, a week abroad, a car in for repairs, or any other break from driving will not cause it to drop or expire. Your rating only reflects your actual driving and only changes when new trips are recorded.