This is the risk of using offline mode. You can check your transaction status to see if the card was declined. If you were offline for two long the sales will expire. (72hours)
There is not unless you maintained a list or have contact information for the customers during this time. It is highly advisable if you are going to use the offline mode that you take a higher precaution on the transactions. It is the risk of having the ability to use offline mode. Personally, I haven't and won't use offline mode because the risk is too great for declines etc.
