No really, they might. It's happened. They won't be deleted from your "purchased music" unless you do that yourself, but they might be removed from your device/computer, renamed, given incorrect art, replaced with DRM'd versions, etc. Read this:
https://forums.macrumors.com/thread...-right-old-mess-of-my-itunes-library.1896446/
Just back up everything you buy. You should be doing that anyway, but this is a case in which being diligent about is going to be pretty important.