Nothing would happen to the music you bought on iTunes or the music that came off of your CD's etc …
The music you purchased from iTunes is connected to your iCloud account so that if you try to purchase it again, it knows that you've already purchased it. In addition you'll be able to download your purchased music through iTunes on you Mac, iPhone, iPad etc …
The CDs are a different story. If you have the songs on your computer and on your phone and you cancel Apple Music, they'll stay there, but if you delete the songs off of every device they're on then they're gone.
Apple Music stores all the songs you add from Apple Music to “My Music”. If you enable iCloud Music Library, then those songs you added off of Apple Music will be accessible on every other device that has iCloud Music Library enabled as well. You can choose to add said CD songs to your iCloud Music Library and be able to play them on all of your devices. If you decide to cancel Apple Music, all of your songs in “My Music” will no longer be available but all the songs downloaded off of iTunes will be, your CDs won't be accessible through iCloud Music Library unless you pay for that separately. You'll still have your CDs on your computer or wherever the physical copy is.
You will lose non of your paid iTunes music as you can re-download them off of iTunes.
You will lose non of your CD music as long as you don't delete them off of every device.