Hi,
This exact same thing has happened to me. The Assets Admin Search Rail has just disappeared and I only get the search text box on searches.
Thanks to kautuksahni , I packaged up what I had on staging in: /conf/global/settings/dam/search/facets/assets/jcr:content , and uploaded it to production and it fixed this issue.
Scary why it would all of a sudden disappear like that, but at least there is a fix to it.
Hope this helps.