(a) Except as provided in subdivision (b) and subject to Section 21110, if a transfer fails for any reason, the property is transferred as follows:
(1) If the transferring instrument provides for an alternative disposition in the event the transfer fails, the property is transferred according to the terms of the instrument.
(2) If the transferring instrument does not provide for an alternative disposition but does provide for the transfer of a residue, the property becomes a part of the residue transferred under the instrument.
(3) If the transferring instrument does not provide for an alternative disposition and does not provide for the transfer of a residue, or if the transfer is itself a residuary gift, the property is transferred to the decedent’s estate.
(b) Subject to Section 21110, if a residuary gift or a future interest is transferred to two or more persons and the share of a transferee fails for any reason, and no alternative disposition is provided, the share passes to the other transferees in proportion to their other interest in the residuary gift or the future interest.
(c) A transfer of “all my estate” or words of similar import is a residuary gift for purposes of this section.
(d) If failure of a future interest results in an intestacy, the property passes to the heirs of the transferor determined pursuant to Section 21114.