If you need more feedback on this topic I offer the following.
Your heater trip logic should be set such that upon cavitation the burners should trip based upon low flow to the heater. Cavitation, which will cause both the flow and the temperature to rise and fall rapidly should be dealt with quickly and the logic should be set accordingly. When the initial cavitation ocurs flow will drop (which should cause a trip) and if the heater does not trip temperatures will rise quickly and heater tube coking rates can increase immediately. Once heat is out of the heater and the cavitation has been corrected it will depend upon the level in the drum being fed as to the actions that should be taken. If the drum level is less than half then cold feed can be re-introduced to the drum and heater temperatures quickly brought back to normal levels. If the drum is close to being full then cold feed should not be re-introduced as the cold feed can lead to excessive foaming and potential carry over. With a full drum the heater outlet should be routed back to the fractionator bottoms and feed brought back to the heater while a drum switch is prepared for and when the new drum has been vapor heated the heater can be re-introduced to the coke drum.