Disposable diapers should last in storage for at least 5 years. I'm sure some disposable diapers that you buy in stores set in warehouses for at least a few years before being sent to the store restocking the shelve's.
I think that with disposable diapers they do expire after so many years probably longer than 5 years and more likely at 10 years old the SAP would probably start breaking down in the diapers.
Other than that disposable diapers should good in storage for a few years. So if your baby potty trained and you still have diapers left over and you plan to have another kid then I would keep the diapers for the next baby since the diapers should be okay to use within a year or two.