What happens when I unsubscribe from iTunes Match?
No, iTunes distinguishes your content gathered from outside the iTunes Store as either Matched up Uploaded. Matches means if found the song on iTunes while Uploaded means it could find the selected song but instead took your copy and placed it in the cloud. The benefit of the former is that Apple's copies are high quality AAC files and will replace your sometimes inferior lower bitrate MP3 in the cloud. At no time does the service concert any item to the "purchased" status however.

Once the service expires, Matched and Uploaded songs no longer can be downloaded indefinitely. The iTunes Match service is essentially the download portion of the service. Once you unsubscribe, you can no longer download any more songs from the service that have been marked as either Matched or Uploaded. Any song you downloaded while iTunes Match was active, you get to keep, though.

More information on iTunes Match can be found here: http://support.apple.com/kb/ht4914