Hypothetically — not that I did this — let’s say someone I know updated their working copy of a file, saw conflicts, hastily clicked “use theirs” then quickly marked as resolved…
Is there any way to undo that and get back the couple of hundred lines of code that I.. er… I mean someone lost…?
No. You’ve lost it.
When you..r friend.. saw the conflicts there would be 2 files on disk with both revisions changes in them. When you clicked ‘use theirs’ you’d have overwritten your WC file with the revision from one of those files. But, when you clicked ‘resolved’ you deleted both the temporary revision files.
So, if you’re lucky they might be recoverable with some undelete software and then you can unpick your WC with those changes (try reverting the the previous revision and then applying the file as a patch)