I believe it was about four years ago when my 2001 Volvo blew an oil seal. At the time this happened I was driving at 65-70 MPH in the mountains of West Virginia. I don't know exactly where it happened, but I did notice that a number of cars that had been running with me suddenly backed off at least a quarter of a mile. After cresting a mountain there was at least a five mile glide down to the next valley, albeit still running at 65-70 MPH.
Once I got to that valley I exited the four lane highway and drove through a small town at 30-35 MPH. There were no obvious signs of trouble yet. Once leaving town and picking up the pace a bit, the oil light came on briefly while rounding a curve, but went right back out as soon as the road straightened out. The engine still sounded fine, but this oil warning started repeating with every meaningful curve in the road. By this time I had a pretty good idea of what was happening, but I pressed on 12 miles to the next town and stopped at a NAPA shop. This vehicle has a six quart oil change and it took four quarts to bring it back to the full mark, meaning I was driving it four quarts low. Granted this is a European car designed to run on the German Autobahn. At the time I was running 0w-40 Mobil 1.
After adding those four quarts, I tried to find a shop that would look at the car, then turned around and retraced the last twelve miles to see if maybe somehow I could baby the vehicle back towards home or at least a shop that knew something about European cars. In sixteen miles of driving I lost another three quarts of oil! Suffice it to say the car wasn't going any farther without repair.
Rolling the clock forward, that vehicle now has another 50K miles on the odometer and is still running strong. Wear metals were running in the single digits until last year, and roughly half the Blackstone universal averages for that engine. Keep in mind that this engine has a large sump, but it seems to me that you probably shouldn't lose any sleep if you were to briefly run your vehicle more than a quart low. The most important word in that last sentence was "briefly" and also note that I never got a steady low oil pressure warning.