Tesco won't shut their store for half an hour at no notice during opening hours and tell you all to wait until they feel like opening again...so your analogy doesn't fit I'm afraid.
Yes they will. A local OneStop (Tesco owned) is often closed because of lack of staff. At a Tesco Express, a computer fault knocked out all of the tills and people were unable to pay. Funnily enough, they weren't allowed to leave without paying, so had to wait or leave their baskets and go somewhere else.
Supermarket analogies are so popular on this forum but so rarely work as comparisons to anything on the railway.