Clerys will not honour your gift card - but there may still be help
After their shoddy treatment of workers, the owners of Clerys don't intend helping customers either.
Those with gift vouchers to spend will find them useless now. However, don't forget if the voucher was paid for by a credit or debit card it may be possible to get a refund through the bank's Chargeback insurance system, which can be claimed on when a company ceases trading.
Contact your card provider/bank (or ask the person who gave you the voucher to contact theirs) and set a claim in motion.