I haven't flown the Merlin, but have flown plenty of twins (with varying degrees of excess power) and I don't think there is any difference in the basic theory. Don't think in terms of how many engines you have, or have failed, simply think in terms of what is the power required (at the moment of failure) and what is the power available. If the power available is equal or greater than than power required, you don't need to do anything much. If the power available is less than the power required, you need to change the power requirement i.e. you need to lower the collective. If the power available matches the power required, but has a time limitation associated with it (30 sec, 2 min etc) then you may need to subsquently reduce the power demand.
At the end of the day - mantain Nr!
