A difficult line to follow and it has taken some time to find a decent supporting explanation, even if it is one which requires lateral thinking. I would certainly agree that there would be a reduction in power and an increase in exhaust smoke. The smoke being a result as said of incomplete combustion. This would also mean an increase in soot contamination of the exhaust system including the EGR system and significantly the variable geometry turbo. Assuming that the Intercooler failures are not a sudden dramatic event but a progressive event - pinhole to crack, the reduction in power and level of smoke may well not be noticed initially. I agree that the engine management system ought to be intervening, however we seem to be referring to mutiple intercooler failures resulting, and an historical element of now prolonged operation at just below a critical level. Having found the following video hopefully it hints at how this engine destruction could occur, particularly if engine mapping has been involved . I have kept in mind that aluminium melts at 1220 deg F and operation at maximum torque. It doesn’t need a particular level to be exceeded for disaster to strike, but an accumulation of occasions when it has been almost reached can result, as in so many cases, in a sudden event following.