Does the illegitimacy of a lease-to-own car contract invalidate the guarantee, or is the guarantor obligated to pay?

We have previously explained the ruling on lease-to-own contracts, and that most of their forms are impermissible. The guarantor is liable. If the contract is one of the permissible forms, then it is obligatory to fulfill the guarantee and to refer back to the guaranteed party. However, if the contract is impermissible, then it must be revoked or converted into a Sharia-compliant contract by separating the lease agreement from the ownership agreement, or by having the lease agreement accompanied by a gift of the car to the lessee after the full rent has been paid. If the company refuses the conversion, then the installments must be paid, with recourse to your colleague for the amount paid.