Hi, a bit of a bug here.
When I drag a guide back to the ruler, out of view, with the intention to discard it, it's still there, at a measurement right underneath the ruler. So when I pan or zoom my stage out, I can still see it. However, I can't grab it anymore, and when I save, close, and re-open the file, the guide is properly gone, eventually.
I work with Animate 2014.1 on a Mac with Yosemite.