If depositors could/had to wait years, there wouldn‘t be a need for insurance anymore in this case.
I feel the exact opposite as you. Now that essentially 100% of deposits are guaranteed indefinitely, there is only downside to withdrawing.
that would alone create some outflow even if the reason is not panic
If anything, I think the events of the last few days could reduce it somewhat. Better to have your funds safe earning little in a Big 4 bank than somewhere else with higher rates but now perceived to be risky.
And in SVB's case, a very small amount of withdrawals was enough to trigger insolvency. (As it forced the bank to sell, and thereby mark-to-market it's long-term treasuries.)
JPM has $500B of cash and cash equivalents on their $3T deposit base. Of which only ~$34B is in actual cash. Even JPM would fall (without Fed backstop) if JPM had that much withdrawals as a percentage of deposit.
Almost all of those withdrawals happened after the bank was insolvent.
SVB had to sell all of their available securities to cover day-to-day customer withdrawals (The problem with being the bank of choice for startups is that they aren't making any money, aren't getting any new investments, but are still spending money.)
The bank run started after SVB started dipping into its underwater long-term securities, and borrowing money, and doing emergency fundraising.
A more diversified bank (Like any of the big four) would avoid this problem, because their regular day-to-day activity would be a ~net-zero balance of withdrawals and deposits. SVB was uniquely vulnerable because of its undiversified customer base, where normal customer activity pushed it towards insolvency.
But I don’t think people realize that no bank could have 25% (and counting) of deposits withdrawn in a day and survive.
If they had still been allowing withdrawals on Friday that number would be much much higher.
That's not "reality" though. The phenomenon of people "panicking" (ie acting sensibly when their savings are at risk and getting them out while they still can) is a fundamental part of the crisis-process of any bank when it is badly managed.
Saying "well if people just ignored history and group psychology and hope nothing bad will happen and risk all their savings by doing nothing, then nothing bad will happen" just isn't remotely realistic.
Silvergate, SVB and Signature were insolvent. This wasn't a fire sale prompting a decline in their asset values, i.e. classic illiquidity. It was their assets being worth less than their liabilities. If it were purely a liquidity issue, they could have borrowed at the Fed's discount window. (As First Republic appears to be doing.)
If the same thing happens to other banks - everyone withdraws, they shut down and the government steps in - the assumption is that their equity will eventually be worth $0 too. So, everyone sells at >$0.
It's not going to be all banks, though.
And there was a bank run because the investors panicked and caused the share price to plummet. Depositors saw stock plummeting, got nervous and pulled out. If this type of thing spreads to other banks we'll have a bad time.
It also simultaneously stepped in to preemptively save similarly-situated [0] banks, though.
[0] to the condition SVB was in which led ultimately to the bank run.