This Reddit poster seems to be in that unfortunate situation. Their father passed away and left a 401(k) plan behind. But they can't get the institution holding that 401(k) to release the funds.

His father cashed out a 401(k ... Now, I'm not a lawyer or tax professional so this is only my opinion, but legally, children aren’t automatically liable for their parents’ debts, including ...

My stepmother appointed my stepbrother as the executor of her will. My father passed away in 2004. My stepmother has a condo and a fair amount of investments, although I have no idea how much she has.