When responding to a thread a couple weeks ago, it made me realize I do not know for certain about when a wav file is committed to disk. Specifically, say I create a new project, insert an audio track, record a snippet, but then do not save that project when I close it... is that audio track still in the Audio subfolder (assuming Per-Project Audio is on)?
 
I always assumed the answer to this was "yes," but never actually checked it. (I assumed once the transport was armed, recorded, and stopped that it was committed to disk.)

yes, it should still be there and that's what the "audio clean up" tool is for, it removes wave files no longer associated with a project.
 
I had a project one time where I got a vocal ensemble together in a room, 8 voices singing to a backing track they were hearing in their headphones.  we did several takes over the span of about an hour.  when the session was over, we started tearing down and someone unplugged the power to the computer!  It was at that moment I realized I had not saved the session!  OH THE HORROR!!!
 
but I went into the audio folder and the tracks were still there!  all I had to do then was import them back into the project and all was well!

But what about this...
If I press Ctrl+Z immediately after the take, does the wav get overwritten by the next take?
For some reason I used to assume that is how it works, but I've never really checked that  by inspecting the audio folder. At least the take number on the clip doesn't ascend in such a case, IIRC.

That scenario, I am not certain, but I think the wave file is still in existence until you save the project.

The only time I have had trouble with the files disappearing is when the power to the board, connected to my laptop with fire-wire, lost power. Sonar dropped out as you might expect but because the audio device disappeared the wave file was never closed properly and written to the disk.
 
That was a bummer.