Well, I don't think neither Wiener Stadthalle nor Wiener Messe will withdraw because of a couple of booked low-profile events. Sorry, these events can take place elsewhere, and Austrian tourism and Vienna economy will also have a say.... the decision just can't be made alone by hall management on behalf of public interest.
I don't think a single ticket has been sold yet for Dieter Nuhr or James Last, and they can all postpone their Vienna dates or go elsewhere....
Well, of course it doesn't look that good for Wiener Messe now with 10,000 liver experts, but who knows....