You'd need to talk with an attorney familiar with Social Security, or an appropriately qualified SSA representative to be sure - but all signs point to the idea that unfortunately Social Security does not work the way your father was told it would. And if he doesn't file to receive benefits the reality is actually much worse than "throwing away free money"! However, this is not due to a complete misunderstanding of the system! Social Security does work the way he thinks in some instances, just that the rules don't apply to his exact situation!
First of all, retroactive benefits come in a few forms:
File and suspend to get a lump only if you really need it - BEFORE the age of 70 only! In this method you apply for retirement, but you tell the SSA to suspend/delay your benefits. You are entitled to full lump sum of the payments you deferred...but at a cost of getting lower monthly benefits permanently (and that also lowers spousal and dependent children's benefits, too - if those could apply to your dad). But note that at the age of 70, Social Security will stop deferring the payments and start paying you the full maximum retirement benefit monthly, with no lump sum. This is a kind of emergency insurance policy for those who want to try to defer retirement benefits, but who want the opportunity to cash out and get the money they would have been getting "just in case".
You can get up to 6 months of retroactive benefits, such as if you wait past your exact retirement age to apply for benefits. But no more: "we cannot pay retroactive benefits for any month before you reached full retirement age or more than 6 months in the past".
As for after-death benefits, an estate can only get benefits that were already due to be paid, which generally means a person died and did not get their benefits for that month, so SSA can re-issue a check to the estate following these rules. But as a person cannot be due a lump sum payment after age 70 (for more than 6 months at most), the estate will only be able to get at most 1-6 months of payments (and 6 months is doubtful - you'll need to ask a lawyer if that much would even be possible). If your father was below 70 and wanted to file-and-suspend, the question of lump on death would be more complex and I don't know that answer - but once you are past 70 this doesn't matter any more as you aren't due a lump anymore.
What about lawsuits?
Given the above, we've established pretty clearly that if you don't claim your benefits within 6 months after age 70, any months of payment you would have gotten are just forfeited to the system. But if you claim the benefits and stick them in the bank, can they be taken?
Well, if a lawsuit is really a worry, then yes these accumulated funds can required to pay a debt - but this potential for loss can be protected against without forfeiting the benefits entirely! This is not very common, but if your father doesn't need the money now he may be able to deposit some of the money into a special partially-lawsuit protected format of the Roth IRA (which has no age limits) as detailed here. If he never gets sued, that's OK - it's still his money! If he passes away, the value goes to his estate and does not disappear. And he doesn't forfeit any of his earned retirement benefits.
It's Not Free Money - It's His Money
Finally, I would like to share one last thing with you and your father. These benefits aren't free - he has been paying a portion of his paycheck for decades into Social Security, and now he is eligible for the maximum amount of benefits per month that he will qualify for - and if he wants to keep working he loses no benefit and the amount could potentially even go up. That's up to him.
But not filing for benefits now will mean that all this money he's been paying in for decades will just be lost - they'll basically just be a tax he's paid out to other retirees. His estate (which means you kids) won't get any of it, either. That'd just be a waste for everyone involved.
If you have continued doubts or questions, I wouldn't hesitate to consult a specialist lawyer or talk with the SSA directly to make sure this is all correct. It's his money, and he has earned his benefits for many years. I very much hope he gets to enjoy as much of them as he can!