Is the money the husband borrowed from the Kuwaiti considered a debt that he must repay, or is he not obligated to repay it because he lost the cost of two travel tickets due to not being provided with work?

Your husband must pay back the money he took from its owner, because it is a debt owed by him. The Messenger of Allah (peace and blessings be upon him) said: "The property of a Muslim is not lawful except with his willing consent," and "The procrastination of a rich person (in paying debts) is oppression." His loss on the two tickets is irrelevant, and it is not permissible to respond to a sin with a sin, for the Prophet (peace and blessings be upon him) said: "Return the trust to the one who entrusted you, and do not betray the one who betrayed you." He should contact the owner of the money and inform him of this; then he should either pay him back his money promptly or at a later agreed-upon time.