From the FAQ
What happens if your upgrade has been accepted, but SWISS cancels your flight?
Your upgrade remains valid if you are re-booked to another Swiss flight subject to availability. Otherwise, we will refund the amount.
Not sure if this one holds - since they "sell" a business class ticket I would assume that standard downgrade compensation should apply. If they enforce this new rule it will also have quite negative consequences for mileage/voucher upgrades ....