You will only lose the ones that were put onto your SD card.
To transfer your files do the following below. (Assuming you have windows if not then if someone wouldn't mind putting Mac on this thread as well.
When you go to your gallery it should say camera, SD, phone, downloads and such, if not then when you plug your notepad (tablet i pressume.) or SD card into your computer wait for the auto-play, if auto-play doesn't pop up then go to my computer and right click (assuming you have windows) on your notepad or SD card and click open auto-play one option should say import videos and photos you'll want to click that option. Wait for the process to compete and all of your videos and photos from your notepad or SD card (depending on...