Ouch, that's quite a hit!

One option might be to move the flights to dates still available in mid May, I'm guessing that they will be cancelled pretty soon (up until May 13th were wiped out in the last few days). It's a gamble, but certainly more likely they will cancel flights in May than in June. As for refunds, well at the moment they are probably going to be hard to get without a mighty fight, but you'd get vouchers that would be valid for 18 months.

If they don't cancel the flights that you rebook in May, you could still move them again for free (if still in the same fare buckets) to later. The 'ZERO offer' of free rebooking with waived fare and rebooking fees finishes tomorrow, but you can still rebook with their general 'flexibility' offer after May, but you'd have to pay any fare difference.