Here are the exceptions, in case you don't have them. Let me know which one you think he meets and we can review. I am assuming you are trying for (i), and if so, you must meet that definition of accidental death, not illness (and you don't mention how he passed away).
"(2) Your relationship to the insured as a wife or husband did not last 9 months before the insured died, but you meet one of the conditions in paragraphs (a)(2)(i) through (iv) of this section.
(i) At the time of your marriage the insured was reasonably expected to live for 9 months, and the death of the insured was accidental. The death is accidental if it was caused by an event that the insured did not expect, if it was the result of bodily injuries received from violent and external causes, and if, as a direct result of these injuries, death occurred not later than 3 months after the day on which the bodily injuries were received. An intentional and voluntary suicide will not be considered an accidental death. [Illness does not constitute accidental death, unfortunately.]
(ii) At the time of your marriage the insured was reasonably expected to live for 9 months, and the death of the insured occurred in the line of duty while he or she was serving on active duty as a member of the uniformed services as defined in §(###) ###-#### [Was he in the line of duty?]
(iii) At the time of your marriage the insured was reasonably expected to live for 9 months, and you had been previously married to the insured for at least 9 months. [You probably would have mentioned this, so I am thinking this does not apply.]
(iv) The insured had been married prior to his or her marriage to you and the prior spouse was institutionalized during the marriage to the insured due to mental incompetence or similar incapacity. During the period of the prior spouse's institutionalization, the insured, as determined based on evidence satisfactory to the Agency, would have divorced the prior spouse and married you, but the insured did not do so because the divorce would have been unlawful, by reason of the institutionalization, under the laws of the State in which the insured was domiciled at the time. Additionally, the prior spouse must have remained institutionalized up to the time of his or her death and the insured must have married you within 60 days after the prior spouse's death." [Again, does't seem to apply.]