Won't help you in this case, but I've started saving copies of all my final assemblies for a project as part files. May not help you at all as you lose all your part creation data. On large assys best to start the save and go to lunch or go home.
Started this after spending 20 minutes refinding all the parts SW had lost on a large assy I'd had open just a couple of months ago. Really looked like an idiot while the engineer stood over my shoulder waiting so he could see how 2 parts fit together.
Nothing had been moved. All the parts were in the correct folders. The computer hadn't changed.
Don't know if others have this problem, but SW will lose track of where files are on an assy I just closed and reopened sometimes. Usually no big deal, but when the files are in a dozen different folders as that assy was it can be very time consuming to refind everything.
Also find this useful as nothing in the assy changes if any of the part files are accidentally changed, moved, renamed, ect.. It's a file I'm sure was correct at the time of the projects completion (extremely valuable). Plus the part file opens faster when you just need to look at something.