Does the contract of mortgage become void if the mortgaged house collapses before the mortgagee takes possession?

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The contract of mortgage does not become void if the mortgaged house collapses before the mortgagee takes possession because its total value has not been lost; its plot of land ('arsah) and debris ('unqud) remain. Consequently, the mortgagee has the option (al-khiyar) if the mortgage was stipulated in a sale, due to the defect and decrease in the mortgage's value. The difference between this and the lease contract is that the lease is a contract concerning the utility of habitation, which has become impossible and ceased to exist, thus invalidating the contract due to the absence of the subject matter. Mortgage, however, is a contract of security related to the physical assets possessing value, which remain.