It would seem good customer relations to find some way to get the waiting facilities (and presumably toilets) open for the waiting time in these situations. Is there not an emergency local authorised keyholder?
Pewsey is peculiarly distant from other stations and not easily driven to from any of them ... so there could be sense in having a local backup in place. The regular
GWR▸ person based there - but for an early rather than a late shift - does a superb job when he's on duty and I suspect would pop down to the station beyond the call of duty if alerted and available.
There was talk last October of appointing (? volunteer) station ambassadors at unstaffed stations in Wiltshire. "Soon" was the word, but in railway terms "soon" hasn't progressed yet.
Good job they weren't coming through the Severn Tunnel and dropped off at the first station in England. That's really bleak, and a long wait for the next stopping train!