Upon the revocation or reduction of the donation by the birth, appearance or adoption of a child, the property affected shall be returned or its value if the donee has sold the same.
If the property is mortgaged, the donor may redeem the mortgage, by paying the amount guaranteed, with a right to recover the same from the donee.
When the property cannot be returned, it shall be estimated at what it was worth at the time of the donation. (645a)