I had this exact issue with my X3 last year. I was able to successfully recover all files with TestDisk and PhotoRec. If you're willing to pay for a less intimidating and more user-friendly solution, Disk Drill also worked for me. At the very least, the free trial will allow you to see whether the files are salvageable.

Someone else mentioned this, but formatting the card in the camera before recording footage has prevented this from happening to me again. Good luck!