(a) If the property or interest devolved to a disclaimant under a testamentary instrument or under the laws of intestacy and the deceased owner or donee of a power of appointment has not provided for another disposition, it devolves as if the disclaimant had predeceased the decedent or, if the disclaimant was designated to take under a power of appointment exercised by a testamentary instrument, as if the disclaimant had predeceased the donee of the power. Any future interest that takes effect in possession or enjoyment after the termination of the estate or interest disclaimed takes effect as if the disclaimant had died before the event determining that the taker of the property or interest had become finally ascertained and his interest is indefeasibly vested. A disclaimer relates back for all purposes to the date of death of the decedent, or of the donee of the power, or the determinative event, as the case may be.
(b) If the property or interest devolved to a disclaimant under a nontestamentary instrument or contract and the instrument or contract does not provide for another disposition:
(c) The disclaimer or the written waiver of the right to disclaim is binding upon the disclaimant or person waiving and all persons claiming through or under him.