Concur with John E - whilst there might be twice the chance of engine failure, there's a significantly higher chance of flyaway following a SINGLE engine failure, which is what we're really talking about. I can't remember ever reading or hearing about a double concurrent turbine engine failure - & before someone finds one, I mean not caused by severe icing or fuel starvation, neither of which would likely happen with this sort of operation, I'd suggest.
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Actually, in the early days of the 76 we had numerous uncontained third stage bursts that took out the second engine, ...
... and the t/r driveshaft, ...
... and all the a/ & d/c electrics, ...
... and then caught fire.
But you didn't need to worry about the fire, because you couldn't fight it even if you knew about it, which you didn't.
Hence that goofy 180 lb "containment kit" in about 1983 or so.