Contacts missing from Adressbook…AGAIN!

Got a call from the wife saying all of her contacts were missing from her iPhone. I checked the address book on the iMac and sure enough they're gone there also. I'm afraid to sync my phone for fear of losing mine also. Any hope of retrieving them?…and why does this happen. We just got back from a a two week trip so the phones had not been synced. I had no issue with my sync…hers..not so good. We do share some of the same groups. I've considered using the "Bump" app to send the contacts on my phone to hers,