If a decision was made prior to issuing the provisional credit that the bank would eat the loss, I would have issued final credit to begin with. You are creating double work.
That said, I would recommend investigating to ensure that the reported error was indeed related to the breach and not something for which the customer should be responsible. Obviously if there is some type of pattern to quickly determine it is related, an investigation may not be necessary. Just issue final credit.
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Life without Jesus is like an unsharpened pencil - it has no point.