The timing of this post is pretty absurd. I'm building a little plastic test fixture box which with a number of AC mains switches. Yesterday, probably for the first time ever, I wondered "huh, what if the metal bat on one of these switches fails...can it easily become connected to mains?". So, did a quick search on Youtube to see how toggle switches are fundamentally constructed to try to understand the implications of a failure.
Found this video:
In the end, I think it really depends on the exact switch you are using. With a hard enough blow directly into the top of the metal bat, seems like the "plastic actuator thing" could possibly get crushed enough such that the metal bet comes in contact with mains. In normal use, if the "round nubs" get worn out enough that they break, you're probably safe because there's still the rest of the plastic rectangular thing still intact. This is solely referenced off of the above video.
At any rate, if you want to use a toggle switch without a properly earthed enclosure, probably best to pick a plastic paddle version.