In a sense you still are, you are on the territory of a Schengen country, its law fully applies, if you did anything that would justify it, you could be arrested by the police, etc. The airport, even the area after the exit passport check is not some sort of extraterritorial area out of reach of the country's laws.
That said, if you stay airside in the sterile departure area, I don't see how you could possibly be deemed to have breached the conditions of your visa. You already have an exit stamp with the proper date and would not have any problems the next time you applied for a visa or enter the Schengen area. If the airports has such facilities, you should press the airlines to offer you lounge access or an airside hotel room to wait for the next flight.
Now, if you need to go through the passport check again, say, to spend the night outside of the airport or catch a plane at another airport in the vicinity, things become more complicated. There is a provision to extend a Schengen visa (article 33 of the visa code) if you have a serious reason but my reading of the regulation is that this is in principle only possible if the new stay would not lead you to exceed the global 90-day limit for short stays in the Schengen area.
If someone needs to stay longer than that, member states still have the possibility to issue a “limited territoriality visa” (article 25) and they may in any case issue a visa at the border (article 35). Both of these are intended as exceptional procedures but the authorities have some leeway in judging what's an exceptional case. Combining articles 25 and 35 would therefore seem to be a fully legal way to grant you some more time in the country where you presently are, at the cost of a bit of paperwork and possibly a fee.
I can also imagine that some border guards would be confused about all this and I am not entirely sure that it would happen smoothly.