Ours did come back. I know this was a while ago, but just wanted to report, bc this just happened to someone else i know with a lot of reviews.
I'll try doing the map search you suggested Linda. UPDATE: No dupes found. Just all about 100 reviews gone.
I've noticed on the Google user forums that one thing that may trigger a wipeout of reviews is having a lot more than everyone else. This is definitely the situation in my friends' case. They have (had) over 100 reviews and are now down to 1. I think the closest competitor had 10. No trickery going on, though. They have a ton of clients and have done a good job soliciting feedback.