If the chain slips off your smallest chain ring, and you have the opportunity, if you will move your der to the largest chain ring it will most likely slip back on itself to at least the smallest, and you can keep going.
However, this, of course, never happens when you have an opportunity of some rolling distance before shutting down and falling off of your bike!!
Anyway, we have all had a chain slip off, especially when shifting from a larger chain ring to a smaller chain ring on a hill.
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