*sound of angels singing*
Like the creator of this post, I too like to live on the edge with only a few GB of free space on my laptop...which has occasionally dipped to the DANGER, 0 GB of space. Both times, my NetNewsWire feeds have been completely deleted. I open NNW and find the reset values which are sports and technical blogs that interest me not at all. The first time, I spent a full day re-finding a lot of the feeds I used to read. The second time, I made my lists shorter. The third time, I gave up. I haven't been reading my RSS feeds for over a month.
But this simple set of instructions has recovered all my lost subscriptions. Thank goodness!!!
Go to ~/Library/Application Support/NetNewsWire/ and delete the Subscriptions.plist file
Open the Backups/ folder, and you will see a list of your subscription files with backup dates.
Copy the latest one back into the NetNewsWire/ folder, and rename it to Subscriptions.plist
Restart NetNewsWire and your subscriptions should be recovered.