Little Belle, there may be some hope of getting your hat back. I took a backstage tour at WDW a few years ago. One of the things they showed us was the area behind the Splash Mountain building where the lost hats, soda bottles, etc. wash up at the end of the day. My understanding is the non-trash items are retrieved and sent to Lost and Found. So, it's probably worth the effort to contact Guest Relations and Lost and Found to find out if they have your hat. Be prepared to give a detailed description (shouldn't be hard, you can provide a picture!). Knowing the exact date and approximate time you lost the hat would be helpful information for them.
Of course, this info may be completely out of date but I figured I share it with you just in case you can get your hat back!
qruthie (the 'q' is silent)