(B) Exception Subparagraph (A) shall not apply where, on the lapse of time, on the occurrence of an event or contingency, or on the failure of an event or contingency to occur, an interest passing to the surviving spouse will terminate or fail
(i)
(I) if an interest in such property passes or has passed (for less than an adequate and full consideration in money or moneys worth) from the decedent to any person other than such surviving spouse (or the estate of such spouse), and
(II) if by reason of such passing such person (or his heirs or assigns) may possess or enjoy any part of such property after such termination or failure of the interest so passing to the surviving spouse, or
(ii) if such interest is to be acquired for the surviving spouse, pursuant to directions of the decedent, by his executor or by the trustee of a trust.
For purposes of this subparagraph, an interest shall not be considered as an interest which will terminate or fail merely because it is the ownership of a bond, note, or similar contractual obligation, the discharge of which would not have the effect of an annuity for life or for a term.
(C) Interest of spouse conditional on survival for limited period For purposes of this paragraph, an interest passing to the surviving spouse shall not be considered as an interest which will terminate or fail on the death of such spouse if
(i) such death will cause a termination or failure of such interest only if it occurs within a period not exceeding 6 months after the decedents death, or only if it occurs as a result of a common disaster resulting in the death of the decedent and the surviving spouse, or only if it occurs in the case of either such event, and
(ii) such termination or failure does not in fact occur.