As you're probably aware, AutoCAD includes an automatic save option to save your drawing at specific intervals. The idea is to create a saved copy of whatever drawing you are working on so that if something unexpected happens since the last time you manually saved your drawing, e.g., AutoCAD crashes, your computer crashes, etc., you'll hopefully have a fairly recent copy saved somewhere.
Autosave files are typically named using a mangled version of the drawing name, ending in ".sv$", e.g., "2170topo_1_978319771_4666.sv$". By default, they are saved to a temporary folder on the local machine but you can choose another location for these files using the SAVEFILEPATH system variable or by changing the Automatic Save File Location in Options/Preferences. If you need to revert to an autosave file, you can go to this location, find and copy the appropriate file to another folder, and rename the extension from "sv$" to "dwg".
Note: The automatic save feature is not a substitute for manually saving your drawing and should never be treated as such. It is a contingency plan for when bad things happen.
That's a little background on autosave – just in case you needed it. I actually said all that to say this …
By default, AutoCAD for Mac writes autosave files to the /tmp folder on the root of the hard drive. This is a hidden folder (so you probably don't see it) and is actually a symbolic link to the /private/tmp folder. Here is a view of the /tmp folder from Terminal:
The issue is that the contents of a /tmp folder on a UNIX-based system (of which Mac OS X is one) are not permanent and /tmp gets automatically emptied when the computer is rebooted. This means that any and all autosave files that might be in the /tmp folder will be automatically erased the next time your Mac restarts.
I recommend you change the location where autosave files are saved in AutoCAD for Mac so that:
1. Your autosave files won't run the risk of being quietly removed.
2. They are easier to find than when in a hidden folder.
As I stated earlier, you can do this using the SAVEFILEPATH system variable or by changing the Automatic Save File Location in Application Preferences: