It's possible to create Collection A which is dependent on Collection B, and then make collection B dependent on collection A. Thankfully it doesn't cause a crash, but Logos shouldn't let this loop happen.
It's also possible to create Collection A which is dependent on Collection B, and then delete Collection B. But collection B remains in Collection A, although it doesn't exist. This shouldn't happen either, and ideally Logos should warn you if you delete collections that other collections are dependent upon.