Lost All Files in a folder because of undo on my mac
If I understand the sequence:


you had files only on USB and no backup of those files
you pasted those files on to the Mac and we don’t know if you have Time Machine or other backup on the mac
you deleted the files on USB
the files for deleted off the mac (undo of paste is the suspect, but in the end, it doesn’t matter how they went missing)


The only saving grace or reason I would keep using a Mac in this situation would be to open Time Machine and see if there are any local snapshots to recover the data. If there was a local snapshot made any time after you pasted the files - they are easily recoverable - even if your “backup external disk” isn’t connected or mounted.

If you don’t have a backup, shut down the Mac and don’t run the OS until you’re sure you will or won’t pay to recover the files.


Recovering an accidentally deleted  folder in OSX - no Time Machine or backup available 
How to recover a deleted file on Mac OS X?