Avoiding turn-off of zero-crossing optotriac
The zero crossing detector in the MOC3063 only inhibits triggering if the voltage across the main terminals (pin 4 and pin 6) is greater than typically 5 volts. So, should the device be previously triggered, the main terminal voltage will be no more than 3 volt (page 6 of data sheet) and therefore the zero-crossing detector cannot inhibit that situation and cause the internal triac to open circuit.


  Is this a safe assumption?


Yes.