I am not smarter than the engineers at Stihl; in a bind, I would use other bar oil if I HAD to get something done - like get out of the driveway...but I stick to Stihl bar and mix oils - I value my saw as much as I like not having problems with it.
In an old Husky, I used to use discount store oils - I was not happy with the bar oil performance, nor with the weird mixing rituals of the cheaper 2 stroke bottles...Now days, I don't mind a little arithmetic, but not when a mistake is going to fry a piston, or foul a plug; ruin my saw or end my cutting day.
The fear of poor outcome (of going with cheap lubricants) nagged me long after the initial joy of saving a few dollars per cord of wood. Cost and price are not at all the same.
In a pinch, I'd use some motor oil or gear oil on a chain - maybe mix some in to get done when you see the bottle getting light and you're almost done. I'd fire the furnace or head to town before I put anything else in my gas.