To build upon web-weaver's and Victoria's responses:
Edits are stored in 1 or 2 places:
1. catalog (always)
2. xmp (if "metadata" saved)
When photos are removed from catalog, so are their edits (permanently).
So only way to retrieve edits is from a backup catalog, or xmp.
Note: xmp is either embedded in photo file, or stored in separate "sidecar" file alongside proprietary raw file.
Rob