I think there will have to be some creative thinking about how to make things possible.
One suggestion I've heard for concerts is that they might have to become shorter - removing the whole problem of the interval. So you go out to hear an hour's string quartet, instead of a symphony and a concerto. It doesn't get the orchestras back into full employment, but it begins to get the venues some income again.
I heard a piece on the radio from someone who went to a Shakespeare play, which in the end didn't go ahead, because the biggest name in the cast had had an accident earlier in the day. Instead, that actor sat on a chair on the stage and entertained the audience with anecdotes, and although they were offered their money back, they felt they'd had their money's-worth. Maybe those in theatre can get thinking about plays which might be do-able, monologues, and other forms of entertainment. It wouldn't be the same, but it would get things going again - and I bet they'd get audiences. Musical theatre would be harder, of course.