I didn't fully understand Wikipedia's explanation, in fact I didn't bother to fully read it, most of my understanding was gleamed from looking at the schematic.
If you shorted the drain and source terminals of the output transistor, it would cease to behave like a current mirror, assuming the voltage across the output is a perfect source, the MOSFETs will allow as much current at the threshold provided which might result in smoke if the power dissipation is exceeded.