One idea is a system recovery from dated restore point.
OR locate the save file in your game's doc folder and right click the gaming folder the save file lives in. See if you can restore it from a previous version.
Your issue is one of the many reasons why I stopped playing games like Fallout and Skyrim. Perhaps one day I'll get back into it however not anytime soon.
gl - If you have to start all over again, look at it as an opportunity to begin again and learn something new. I usually take my time and it's a grudge for me to take on a major quest because of these types of issues.