From the perspective of the card network and the merchant, there is no difference here. The card network has a contract with the issuer, so all transactions, in all scenarios, are always first paid by the issuer. It’s then the issuers problem to figure out where they get the money from.
It’s entirely possible to perform transactions on debit card that will place the account attached to it in a negative balance, and for the person owning that account to vanish. The card issuer is still on the hook for the money, neither the card network, nor the merchant, care if the issuer recovers the funds or not, they always get paid.