What happens if you Relink and point the missing file to the folder that contains the actual file? I've done this with hundreds of files in the case of projects that were moved to other drives, and it can work. It's much better in Resolve 12 than it was with v11.
I think that's what I tried to do. I right clicked on the clip(s) and chose change source folder. I picked the actual folder and it wouldn't relink. A few clips (from different rolls) did relink that way. But there was one roll that refused and I had to do each clip manually by re-importing and force conforming.