This is the first forum that comes up on a search for reinstall fallout 4 so I want to post this info here in case someone like past me comes upon it and gets the wrong idea. I've seen this advice a LOT about abandoning saves and after months of intense modding with over 400 mods I can tell you that it's very very WRONG. I have not come across a save game I was not able to recover even after revamping a ton of mods and installing ENB's etc. It all depends on how much time you wish to put into saving it and/or small glitches you are willing to tolerate.
Anyway here are the steps from Steam Forums :
First CUT and PASTE your save folder to somewhere on your Desktop or anther Drive with lots of memory, if it's too big just Ctrl select a few saves and put them somewhere then purge all your mods if you use Vortex just hit the Purge button wait a minute then close Vortex.
1) Delete \Steam\SteamApps\Common\Fallout 4 and all subdirectoris.
2) Delete \Documents\My Games\Fallout4
3) Click Steam | Library | Games | Fallout 4 | Properties | Local Files | Verify Local Game Cache.
Then download all or most of the mods you used for those saves, again if you have Vortex just hit the Deploy button and you're done. Find your new fresh save folder and copy/paste your backup saves there.
Remember to configure all your settings and .ini files etc. If you have vortex this is easy as it saves those and you can copy them to your new instance.
