Cards that can be used in multiple shops are categorised as electronic money gift cards and are governed under different legislation (see here).Well then if I head off to a kiosk in Liffey Valley and buy a voucher and there's a little label on it saying that claims ultimately fall on a voucher company in Lithuania, that doesn't invalidate or compromise my rights as a consumer if it later turns out that there's something wrong with it.
Your rights are similar in the case of a voucher bought from a single shop that closes down. You're an unsecured creditor with little chance of getting anything.