I opened a project I'd worked on a few weeks earlier and was a bit surprised to see a couple of guitar audio tracks missing. The final mixes, etc. are still there but all I can think of is that I must have had a brain fade moment and deleted them after mixing down...very annoying and stupid.  I do save and date versions of projects as I go, but I must have messed that up also...
It's not the end of the world because as I said, I have the mixes.
But I was wondering if deleted audio tracks stay somewhere, just flagged as not part of their original project? 

Not sure John.
 
Have you had a look in the Audio Folder?

If you have the preference set to save audio files "Per Project"  then all of your audio will be in the audio folder inside the project folder,  otherwise you'll have to sift through all the files in your Global Audio folder..
 
Sonar is "non destructive",  so whatever you do to a clip, even delete it,  the base audio file will remain intact.
UNLESS you tell Sonar to clean the audio folder...  in which case it will remove anything which is not used in the project...
 
To recover a deleted clip, use the media browser to audition the files in the audio folder until you find the one you "lost" then drag it back into the track.  You'll have to redo any editing, this is equivalent to reverting back to the original take.

Backups? Acronis?