AB would have the money and QF has not been paid yet (aside from JV it is paid after the sector is flown). You would be an unsecured creditor of AB. Often airlines will fly you on such tickets without payment but you need to check with QF and it is strictly a goodwill gesture. Otherwise you go through the bankruptcy proceedings for reimbursement (which looks to be slim for AB). Depending on your country of purchase for the ticket there may be additional legal protection. It sounds like you are in Germany in which case you are fully protected fwiw.