NO, the circuit will not breakdown under 16V regardless. Since the diodes are in series, if a breakdown were to occur, both diode must break down. Think about this way, when Diode A breakdown, that means a high current would pass through Diode A. If Diode B is connected in series with Diode A and a high current is going through on Diode A, the same current must go through for Diode B as well. If high current has to go through Diode B, that means Diode B must breakdown as well.
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