The oil in the Bandit is just not used for lubrication but also for cooling. Running the oil low enough not to trip the sensor will not cool the bike properly. You're probably %100 fine but if you ever rebuild check for scoring on the cylinder walls and I'm sure the piston rings didn't like it either. Best to always keep the oil level midway or 2/3rds between low and Full in the window so it's high enough to cool/lubricate the engine but not too full to put unnecessary strain on oil seals. If it started back up I wouldn't worry about it too much at low rpm like idling the oil pressure is low and with low oil it just makes it worse which adds more friction and heat so thats probably why it stalled. These engines are hard to kill permanently, although if you did it would be a perfect excuse to put a big bore kit in.
For me I use semi-synthetic. Because it's a wet clutch and the bike has so much power I don't use full but with semi-synthetic it gives you a slight edge over regular dino oil if you're semi-lackadaisical when it comes to checking oil, etc. You also get a few more thousand kms before you have to change it out which helps the slacker factor in me.