Before you re-import, I think it would certainly be useful to try to work out exactly what went wrong....if there's a flaw in your workflow (or basic understanding) it would be better to fix that now to stop it repeating itself further down the road. Files shouldn't 'just disappear', so something clearly went wrong, we just need to find out what.
As Beat suggested in his earlier post, giving a step-by-step account of your workflow in relation to importing would be a good starting point....