This part is not actually that much different with respect to banks, where the cushion is the equity (the stock). Also, if I'm not mistaken the debt securities (bonds) issued by the bank are below the bank account claims, so that's your regular customer cushion too.
Bankruptcy is essentially drawing a horizontal line across the pyramid of liabilities, where everyone below the line gets nothing, everyone above the line gets fully paid back, and everyone on the line is the new shareholder. This line is called "fulcrum".
The difference is in government oversight (regulations) and the social agreement that bank accounts will be bailed out. Because of the former the latter rarely happens (yes I know, 2008, but this concept has been around for a century and a significant minority of protected liabilities such as bank accounts have had to be rescued since then world-wide).
Bankruptcy is essentially drawing a horizontal line across the pyramid of liabilities, where everyone below the line gets nothing, everyone above the line gets fully paid back, and everyone on the line is the new shareholder. This line is called "fulcrum".
The difference is in government oversight (regulations) and the social agreement that bank accounts will be bailed out. Because of the former the latter rarely happens (yes I know, 2008, but this concept has been around for a century and a significant minority of protected liabilities such as bank accounts have had to be rescued since then world-wide).