If they do not find the body, what happens to death benefits like insurance and living benefits like pensions and social security?
It depends on the circumstances. Since we're talking about diving, I'll stick to that. Basically, it comes down to common sense and often the court or 7 year rule. Obviously fraud is a concern for life insurance companies and you can bet they will investigate what happened. Beneficiaries will want to provide any and all evidence. Travel and float plans, Coast Guard and law enforcement search and rescue reports, media accounts, etc. Once it's been deemed the event actually occured and survivability is essentially non existent, acquiring a death certificate and benefits will move forward pretty swift. Despite the rare occurrence when someone has survived for an excessive amount of time on a disabled vessel or island, for the most part we know if someone is not found timely they never will be. The burden of proof lies with, did the event take place and has the time for survival expired.
Now, this can become more complex if you have a situation where, say for example, a solo diver who rarely communicated his/her dive plans or when he/she would dive. People are going to question is this a scam or legit. In these cases, you may need to seek relief from a judge to order the coroner to issue a death certificate, but you're still faced with burden of proof. Sometimes a sworn statement will be required. If that doesn't work, then your final recourse is the 7 year rule, maybe longer with substantial estates.
Here you can read more about it.
Declared death in absentia - Wikipedia, the free encyclopedia
Now, more specifically in terms of assets and simply for the sake of this discussion, if your life insurance policy excluded scuba diving, your beneficiary will likely not receive the death benefit. However, again it depends. The issue here is did the victim die while diving or some other related reason. This increases the burden of proof because perhaps the vessel capsized after diving. Locating dive gear would be paramount to prove the death was not a result of diving. You can see how this can get complicated.
As far as beneficiaries receiving social security benefits, that depends on several factors. For example, do you have enough credits, do you have minor dependents that would qualify for Mothers or Fathers benefits, etc.? But again, it all goes back to the aforementioned issues in my first paragraph.
To add more value and information to this post, there are some important things everyone who has assets needs to understand. Any titled asset will pass one of three ways. By will, by contract or by operation of law. You can read more here on my website.
http://www.jamesspicuzza.com/estate_planning
It's my belief everyone, not just divers, should have their affairs in order, which includes a solid estate plan. Every day is a gift and even Jesus Christ himself did not make it out of this world alive.