If it's a societal event, then yes, you can't rely on safe deposit boxes, just like you can't rely on your bank account. You're better off shoving cash under your mattress and stacking brass and lead.
But if it's an individual event, then your home itself might be a target, and safe deposit boxes might mitigate your risk.
So you really want to do a little bit of all. A month's worth of cash safely hidden in your home. Another in an easy-to-access account at your bank. Another in a deposit box at a different bank.
If it's a societal event, then yes, you can't rely on safe deposit boxes, just like you can't rely on your bank account. You're better off shoving cash under your mattress and stacking brass and lead.
But if it's an individual event, then your home itself might be a target, and safe deposit boxes might mitigate your risk.
It's all about tradeoffs.