I don't think the 5 euro fee for the navigo is refundable. The 3 pound fee one pays for the london oyster card is refundable.
[There is another form of the navigo, for paris residents, which does not charge a fee...is this still the case?]
No, the 5-euro fee is not refundable. The pass is good for 10 years, though, so it can be used during future visits as well.
The regular Navigo for residents is still available. You have to submit an application with a local address, and the pass will be mailed to that address (usually within a couple of weeks, but that may vary).