The fact is that you will have half as many engine failures with a single, other things being equal.
But they are not necessary equal. Engines don't scale geometrically and larger engines are more complex (more blades, for instance). Components such as disks may be more heavily loaded and damage to the airframe more severe. (QF32.)
That's also part of the reason that large engines may have a lower thrust/weight ratio than smaller engines (compare the F414/EJ200 with an F110, not to mention F135). Two engines are shorter (nice fit for a delta) and when you get to a single large engine, arranging all the systems around a hole the size of an L.A. storm drain is no fun at all.
And while some single-engine failures on a twin may be catastrophic (it sounds as though the most recent F135 failure was bad enough to do that), the great majority of power-loss events on a single-engine fighter will result in loss of aircraft.
Last edited by LowObservable; 12th Aug 2014 at 17:32.