I have flown on Tristar ferry flights with an engine inop. It is not recommended, and the ferry range was about an hours flight with a RB211-22B, or two hours with a -524.
Hmmm, the poster must have worked for operators with rather poor maintenance/performance.
Standard body L1011 aircraft, RR RB.211-22B powered, had a usable engine inop ferry endurance of four hours.
Five hours for -524 engines.
IE: not a problem at all, provided of course that those flying these aircraft knew what they were doing.
Of course, it very much depended on ambient temperature of the departure airport, temperatures aloft during ferry, terrain requirements, etc but was certainly possible....and not all that difficult.