Is it possible that the alternator "jammed" internally and the sudden stoppage ripped the pulley off and broke the belt? I have seen that happen, in which case the alternator is history. If the alternator is original, I would replace it on principle, anyway, with a Bosch rebuild. Beware of the cheap rebuilt units!! $319 is the list price for the Bosch alternator. You can buy it online for less than half that price, delivered.
You really need to identify the cause of the failure.