As long as you selected <Remove from Lr> and not <Delete from Disk> your images will still be on the hard drive where they were before.
Right-click the folder in question (in the Folders panel in Library) and select <Synchronize Folder>. This will re-import all image sthat are still on the hard drive in this folder. But it will also remove any photos from Lr that are not on the hard drive but still in the Lr catalog.
Alternatively you can import the removed photos via the <Import Dialog>. Make sure that you select <Add> at the top center (this will add the photos to the catalog but leave them on the hard drive where they currently are) and also check <Don't Import Suspected Duplicates> (top right).
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.