This used to happen on my Incredible, the photo's aren't gone the phone is just looking for them in the wrong spot. The best way to find the pics is to connect your phone to to your PC where you can see both drives of the phone, SD and internal, look for the DCIM folder and photo's will be located there. To change the settings of where you store your photos, while using the camera you will see a tab on the side of the screen, tap this and at the bottom there is a settings option, you can change this from SD to phone storage depending on where you would like to store your photos. After you have changed this I would assume that the phone will start looking for the photos in that folder. All of my pictures were still there and I moved them all to the SD card and changed the settings in the camera and have had no problems since. You may also want to sync them to Dropbox or Google drive or just back them up to your PC to keep them safe.