Nothing, just don't make a habit of it.
you will have coolant in your passenger front floorboard and when you turn your heater on your windshield will fog up
after you fill the coolant bottle, tap on the side with a screw driver, your float is sticking, this also happens with the washer fluid bottle. if that don't work check your wires going to the bottle
Your windshield gets really greasy and you feel silly..
both lights, the check engine and the low coolant light need to be reset and only a GM dealership can do that because they are the only ones that have the codes
The belt will squeak until the coolant wears off.
The remains of the old coolant can cause the new coolant to fail. Using the wrong type of coolant can also damage the engine.
The coolant leaks out.
It will squeak
It leaks coolant.
After coolant is added run vehicle to normal operating temperature and re-check coolant level
Nothing will happen if you drain the cooling system and replace the coolant.