Define "appears to have died"? As in the display no longer powers on or anything? Whilst it is possible that probing the DIN outputs could cause unit failure, it is very unlikely, I mean, a human finger is far more 'dangerous' from the electronics' perspective than a DMM or oscilloscope - lower resistance and higher capacitance producing far more severe ESD (electrostatic discharge - essentially a static shock that can damage electronics before it becomes feelable to humans).
More likely it is just coincidence as these are old units now.
As an aside, if the display does still illuminate, try turning the volume to maximum - you may be able to hear audio very faintly, in which case the preamp might be 'nuked'. Having said that, you should still be able to hear the speakers 'pop' as the external amp gets turned on... I guess if not, then perhaps it's the control signal and/or associated circuitry that has failed.
Equally, it could be coincidence and simply a dry capacitor, corroded PCB trace, cracked solder joint, etc.
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