All Sonar files are on my C drive, which is getting full.  I have lots of room on my D drive and want to move my entire set of music related files to the D drive.  Since Sonar creates audio folders files with every project, I am very concerned about how it will detect them if they're not where Sonar "saw them" in the past.  Am I needlessly worried about this?  Or will I have to tell Sonar where to find the audio files for every project I open after such a migration?

No.  I work with 2 computers and have multiple copies of folders on multiple drives. 
All you need to do is copy the whole folder and then set your pathways to go there instead of C drive. 
First you should have everything backed up to a external drive.
 
My system is I have containment folders sort of like albums. In those are folders for each song. 
My biggest folder is for my Backing track songs which has about 180 folders ( songs) in it right now. 
Each song folder has the CWP, Audio, as well as the lyrics, sometimes a MP3 of the original for reference, and I keep a Midi file as a back up for future proofing. Everything to do with that song in one place. 
 
I work between 2 computers and recently started doing a "save as" to One Drive. The songs are all pure midi so not big files. The CWP files store all the midi as well as the whole page layout and VST, etc used. 
I just open the file on my laptop. mess around and then save it back to One Drive. 
 

Thank you, Johnny V.
After seeing your reply, I moved all the files and changed the default file location for projects to a folder on the D drive.  I'm happy to say it worked and I really appreciate your help!
Randy

Did you back up too??

Yes, I did, just in case something went wrong.