The drivers would stay overnight in accommodation. Sleeping on the coach would be uncomfortable and lack certain facilities. Some touring coaches actually have sleeping facilities located underneath the coach, opposite the toilet, but the NX levantes don’t have these. Some NX work involves drivers on a 4 day rota, where they are away from home for 4 days at a time.
I know when Trathens had the Astromega's on the Aberdeen service there was a kitchen, toilet and such but wasn't aware that some had sleeping facilities.