Was it a trigger or batch campaign? If the latter - and it was set to only run once (and no wait steps), you can pull up a lead record of someone who qualified and check the activity log to see if specific activity that was part of this campaign is included.
Now vote here:
I suspect the leads ran through. Try a smart list either with the original list, if possible, or use MEmber of Smart Campaign, which may or may not work.
You can ask Support or check the Audit Trail to see if you can recover some details.