yesterday my wife encountered this problem on her phone which led me to this site. There appear to be quite a number of people with the same issue but little resolve/resolution aside from if the phone was backed up.
my wife never backed up her phone on itunes, icloud, nothing. so today i tried plugging it into her computer and for whatever reason, all the contacts came back. this was not immediate however.
i dont know if this will work for anyone, but i figure posting a RESULT/FIX might do some good.
these are the steps i took:
-plugged phone in
-went into itunes
-went to restore phone and unplugged phone immdediately after the restore began (i clicked on that by mistake, but the phone did kind of a reboot similar to powering off and powering back up)
-went back through the process and created a "new phone"
-from there i synced everything up and left the phone plugged in.
about 2 hours later she started receiving text messages and noticed a name and not a number on the lock screen. we checked the contacts and they all came back for whatever reason.
i never backed up my iphone either and after reading these horror stories, all our stuff is now backed up.
Hope this helps