> Well, the diode did as it was supposed to, and prevented the reverse-polarity from damaging anything of vital importance.

I don't think so. If the diode were being used to prevent reversed polarity, it would simply have not conducted. If it were a normally-reverse-biased shunt across the power supply, then blowing it would have left the laptop unprotected but otherwise functioning (and it would have had to blow something else in the process, like a fuse). So I suspect it was intended for something else.