I was always curious what would happen if you lost the other good engine
I have travelled on two Tristar ferries. The concensus was that in the 90 secs between take off and V2, you would go down!
Because of this we used to do full boroscopes of the two good engines first.
Procedure was one minute at full power on the good wing engine, then back to idle. Then one minute at take off on Nbr 2, then release the brakes. Feed in the good wing engine at 60 knots, and keep the N1 aligned with the ASI.
There is no V1!, rotate at Vr and pray.
What kind of 4 eng airplane you need to ferry?
BA normally ferries B744 back to LHR for engine change when required. It is cheaper than sending out all the equipement and engine.