Is a wife obligated to take out an interest-bearing loan to save her husband from debt, given that they both know it is forbidden, and in light of his threat of divorce should she refuse?

It is not permissible to commit major sins such as usury under the threat of divorce; for divorce is permissible, while major sins are forbidden. The wife must advise her husband and seek help from righteous people, and she must not obey his command to borrow with usury. If he insists on divorce, she should seek Allah's help and supplicate to Him. "And whoever fears Allah – He will make for him a way out and will provide for him from where he does not expect."