Hello there @aSushiLegend!
That is a very unfortunate situation. From what you are describing, the most likely outcome is that the link between UE and your external drive was interrumpted, leaving your folder either corrupt or empty.
Possible way for recovery would involve checking for any other .uproject files still present. As well, check for any backups or autosaves. Possible locations are:
YourProject/Saved/Autosaves/
YourProject/Saved/Backup/
Library/Application Support/Epic/UnrealEngine/Saved/
Users/YourUser/Library/Application Support/Epic
Last steps would be to check Trash, or test with any file recovery tools. Hopefully, part of the missing data can be retrieved.