Deleted photos completely disappeared

Restore photos from your backups.

For the future, if you do not want to delete the image file from disk you can Delete to take the image out of the Catalog. Then in the prompt window choose [Remove] (only) option - instead of [Delete from Disk] (which both removes from catalog and deletes from disk). If you do not see this option presented, you may have clicked 'always do this'. There is an option in the Settings to 'reset all warning dialogs', in which case all such choices will be again prompted for.

When something is deleted from disk, whether or not a 'trash' / 'recycle' record is kept (or not) depends on various factors that are specific to the particular storage type, and sometimes, on its settings - even, as to remaining space on the disk / a maximum retention quota.

Personally I think it's better not to rely on the 'trash' if you might later want to retrieve something:

•  Do not delete it from disk (just remove from Catalog: if you had told LrC to write out its edits in XMP, those edits will remain in the file system and would re-import along with the image if you ever changed your mind, and wanted it back in the Catalog).
• Do delete, but having protected yourself with frequent suitable backups to elsewhere of your disk storage, such that any accidental or regretted deletions would be subsequently recoverable from there. no system qualifies as backup IMO unless you can do this. Thus, continually syncing the storage to mirror additions, modifications and deletions exactly elsewhere, might not qualify for that reason.
• Manage space in some other way, for example (perhaps on a yearly basis) one can 'cull' rejected or low-rated images and their associated files out of the Catalog, by exporting them selectively 'as catalog' to an archive location,  including duplicates of the required files alongside that archive catalog. Then this same set of images can be fully deleted from your working setup including deletion of their files, using the self-same selection that you have just used for the export-to-archive procedure. 

Lightroom Classic does not delete photos from disk unless you tell it to do so. What most likely happened is that when you imported the photos into Lightroom Classic, you inadvertently moved them to another location. That is one of the options in the import dialog (top middle of the dialog). So the photos are now in that new location, not in the old location on the SSD. Where that new location is I can't tell you, but it might well be the Pictures folder on your internal disk.