re engine-out ferries.
Even on triples and quads it is not a simple matter. Some airlines will not allow their own crews to ferry out a 747 with 3 engines but will call in a team from Boeing to do the job. Insurance plays a big part in deciding.
IIRC China Airline had a problem with an engine in Manila (747). They elected to ferry the airplane out and it ended up in the mud.
I believe the ferry was required to to an engine damaged by a pod-strike but I am unable to confirm this. This was in the early 90s or late 80s. the runway excursion was due to asymmetric thrust.
Anil