Is it permissible for the insurance company to pay off the usurious loan on behalf of the deceased, or are they not prevented from doing so, and the loan is paid from the salary?

Usurious loans and commercial insurance are forbidden. If a contract for insurance has not been made, it is not permissible to enter into one. If the contract has already been concluded, it must be annulled if possible. If annulment is not possible, then you are only entitled to the amount of the premiums paid from the commercial insurance.