That's two separate questions:

And I assume from the wording of your question that he is either National Guard or a reservist, since only active duty servicemembers need to "reach retirement age" before drawing a retirement pay. (That age is 60, with a few exceptions).

1 - When he was divorced from his first wife, his military retirement should have been divided along with all other "property" of the parties. So he (you) need to go back and look at the divorce decree. What does it provide for the division of his pension?

2 - Then, as to the second half of your question: what happens when he dies? In simple form, the military pension dies when he dies, unless he has expressly provided otherwise using a program called the "Survivor Benefit Plan" (SBP). The SBP allows a servicemember to agree to take less than full retirement, in exchange for the military service to agree to pay a portion of his retirement pay to a surviving spouse if he dies first. For the reserves or National Guard, the rules get a little more complicated, since a retiree can make an election for SBP immediately upon reaching retirement eligibility, or defer making a decision until the point where he reaches retirement age, and each of those options has varying provisions for substitution of a surviving spouse. There are strict rules for declining SBP coverage, and in general if a servicemember is married when he/she must make a decision, the other spouse must concur in the election or else SBP is automatically ordered into effect.

So you need to gather the orignal divorce decree, and elect/decline /defer papers completed at the time your husband qualified for retirement (the so called "20 year letter"), and meet with a qualified legal advisor. I would recommend he contact the nearest military installation and make an appointment to meet with the Legal Assistance Office or the Retirement Services office. If he was National Guard, there should be advisors at the State Headquarters.

If you decide to consult civilian legal counsel, look for a lawyer who is former JAG (Judge Advocate General). They will know exactly what I am talking about and will be able to help you with maximum efficiency.