I have flown a 3-engined ferry - from Kinloss to St Mawgan. It is no big deal, especially with close-coupled engines. With the rules in force at the time, the Thrust-to-Weight ratio was huge; far better than most op or training take-offs, as you would expect. Why didn't we change the engine at ISK? They had none to spare that day.
Losing one on task is also fairly straightforward. The captain on the spot would consider all inputs and decide whether to continue on task or not. The twin-engined crew would simply not have that option.