Comment by TacticalCoder

Bank vault can be key+combination (eg three letters) or dual key or others. For example in a dual key: one key from the bank and one key being your own key.

If a key is lost, you go and prove your identity (easier if any bank employee is familiar with you) and ask for a new key. A date is set and a locksmith shall come, you are next to him and next to the bank employee while he uses the bank's key and lockpicks your lock. Then he configures it for a new key (or replace the lock).

It's cost you something like $300 or whatever.

Source: been next to locksmith opening a bank vault, twice, in two different countries. Once for a bank belonging to a deceased family member (we had the key but not the three-letters combination) and once not because I lost my key but because the bank's lock (on my vault) went defective.

So it's not "my key from the my vault at the bank melted during a housefire, so I can never access my vault at the bank anymore" nor is it "I forgot my three-letters combination, so until the end of the universe that bank vault shall stay locked".