I'm always really scared for that to happen one day when I'm away from home. I wear a pair of 4-year old mary janes, and the straps have broken about 4 times already (always when I was around the house, luckily, cause they're a size too big and they fall off without the straps!) so they aren't exactly very sturdy anymore. I'm sure if I give them a good pull, the straps would come off just like that!
Apart from that, the heels are coming off too! And the back of the heel is literally 1cm shorter than the front! And on the inside, the metal things that keeps the heels in place, have come through the sole
But I refuse to stop wearing them until I've found another pair of perfect mary janes!