What happens if a wire transfer is sent to a bank account that does not exist?

Pretty much the same thing you would expect trying to deliver a parcel to an address that doesn’t exist. At some point in time, someone will try to find an account to credit the amount. When such an account cannot be found, the last institution to send them the money is notified that the credit cannot be done, and hence, standard operating procedures are looked at what needs to be done to ‘reverse’ the transaction and send it back to the sender.

The money is never lost.