Just guessing but if this agreement supersedes all others, there are likely to be some other changes. Otherwise there would be no need for it. Understand your original contract is binding unless you sign this one. You should discuss all of this with the attorney. It might also be worth your money to have a contracts lawyer review and explain the entire contract before you decide whether to sign it.
If your discharge was less than 15 years ago, you apply to the Discharge Review Board for your service. If it was more than 15 years ago, you apply to the Board for Correction of Military/Naval Records for your service. But the law presumes your discharge is correct. You have to prove it wasn't, or that it is "unfair." Your best bet is to have a military law attorney review your documents and advise you on the best way to proceed. Often the best route is to wait.
When I did wills as an Army JAG, only the clients kept a copy. We did not. So unless you put it in a safety deposit box or on file with the state registrar of wills, it is probably gone forever. Best bet is to start over.
I am very sorry to hear of this tragic loss. Unfortunately, I don't think any such law suit would be possible due to the long time that has passed since then. And even if that were not the case, you could only sue the individual Marines (which would be fruitless) as opposed to the Marine Corps.
A couple of things: First, don't post any more details about this on an open forum. Second, do not make any more statements to CID. If they ask to speak to you, tell them you will not make any statements and you want a lawyer. Finally, go to TDS and speak to a military defense counsel. They are allowed to extend you past your ETS if they are looking to court-martial you, and based on what you are saying, I think that is likely. You should also consider retaining civilian counsel who is...
The short answer is yes, one can be charged with DUI even though they are not arrested and did not have their rights read to them. The longer answer is that if your husband is facing a court-martial he needs to seek base legal counsel and consider retaining a civilian attorney.