That's not what happens. Let's say 100 clients each deposited $1 in the bank, and the bank loses $20, so only has $80 to pay out when liquidated.
Let's say half (50) depositors withdraw their funds early, they each get $1 back. So now the bank has $30 in assets and has to pay 50 people. Suppose 20 people demand withdrawals, and the bank pays $20 to them. Now the bank has $10 and has to pay 30 people.
I admit that I don't know when/whether a bank can actually refuse withdrawals in such situations, or when bankruptcy proceedings are triggered, but the earlier you withdraw the less likely you're going to lose money, and the later you withdraw the more likely you'll lose a significant part of your deposits.
Sure your calculus still works out on average, but I'm not sure that means anything and it's no consolation for the ones that reacted last.