We have 3 Hampton Bay fans, the most expensive was $140 and the least expensive about $50. I'd have to look up the warranty for the older two, but we just bought one last week, and it has a 15 year warranty. Nobody offers a 15 year warranty unless they are sure their product will last that long. The warranty, of course, is usually limited to certain things like manufacturing defects or failure. If a power surge or incorrect installation caused it to short out they won't cover stuff like that. Your best bet is to contact Hampton Bay directly. Most likely, you'll need your warranty card info and/or your receipt, and things like the product model# and serial #.
No, the store won't take it back. Most stores (not just Home Depot) have a maximum return period - some are 14 days, some are 30 days, and a very few are 90 days. After that, you return the products to the manufacturer. No matter where you buy it. Home Depot's policy is 90 days for most items, which is rather generous. Their store policies can be found here: http://www.homedepot.com/webapp/wcs/stores/servlet/ContentView?pn=Return_Policy&langId=-1&storeId=10051&catalogId=100
I really doubt Home Depot will miss your business, but dissing them because they won't take back your fan after more than a year is a silly reason to not shop somewhere. If you've shopped there as long as you say, then you should be well aware of store-return policy.