Just one quick thought from my side:
SWISS did not make the decision not to fly, it is more so that they are legally not allowed to fly due to the Government closing down all airports and airspace.

So, IF there is an entitlement based on 261/2004, could SWISS claim back all expenses from the Government of each state that closed down the airspace and airport....? And would that mean that Airport charges and ATC charges will rise because that's how every Government would try to recollect this expense.......