So,  I created a lead with harmonies in the back end of a song and then, on Saturday, I was working on the same tracks at the front end of the song adding lead and harmonies.  I burned the song to CD and was listening to it on the way to work when I realized that I had mistakenly deleted the harmonies at the back end of the song.  I always have versioning on so I'm pretty sure I have the deleted clips.  But, what's the best way to get them back into the current version of the song WITHOUT losing the work I did on Saturday?  ...HELP!

Open the current and an older version of the project. Copy and paste the parts needed from the older version into the current version.

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Open the current and an older version of the project. Copy and paste the parts needed from the older version into the current version.

I've not opened two versions at the same time before and was not aware that was possible.  How do you switch from one version to the other?  Are there separate widows or what?  How does SONAR keep different version unique from each other?

You just click each project to focus in on it as this will let you switch between the 2. Just open both and you will see.

As long as "Only Allow One Project Open at a Time" is not enabled in Preferences > File > Advanced, SONAR can open multiple projects at a time in the same instance of SONAR. After opening the projects, click on the "Restore Down" icon on the far right-side of the main menu. Both projects will be visible inside the main SONAR window. SONAR keeps the project files separate by their full path names.

I took a look at the help file referring to revisions.  The help file says I can "revert" back to a previous auto-version but it doesn't tell me how to open an auto-version without "reverting" the project back to it....?

If this is a version created by SONAR, the versions are stored in the folder with the current cwp. Open the folder containing the project in Windows Explorer. The versions have a time stamp appended to the current cwp name. Pick one of the versions, copy and rename it to a file name with a .cwp extension in the same folder. Having windows file extension visible in Windows Explorer may make this process easier.
 
If this is too much Windows processing, the SONAR way would be to perform a "Save As" to a different folder with the current project and roll back the old project to a previous version.

I got lucky and found a saved copy from a month ago that had the parts I needed.  Thanks for the help everyone...very much appreciated!