Maybe this exists in recent firmware, but just in case:
Note: obviously (for the reason I'm describing) one shouldn't leave the printer unattended. Still, we're all human, I think.
Apparently I forgot to actually start the print last friday - I merely told the printer to heat up, and never told it what to print.
So it heated up to 250/100 and stayed that way.
All through the weekend until this morning.
Would it be possible to implement some sort of timer that is started as soon as the printer heats up and gets reset every time it actually prints, to shut the heater down once a time limit of inactivity is reached?
 I am happy to report that there seems to be no damage. The nozle had a crisp mound of ABS on the outside, but once I removed that and heated it up again, the filament flowed freely, as before.
The first few centimeter were almost clear to beige in color, no doubt because all the coloring has been burnt out. I did a few flushed to be sure, and started the next print.