What area of the brain is probably affected if a person stops breathing?

The Medulla and spinal cord is responsible for controlling the body's vital functions such as breathing, blood pressure and heart rate. So, if a person was to stop breathing then, not only will it affect the entirety of the brain (as the brain needs oxygen) but there may be damage to the medulla and spinal cord - which can be fatal. 

Hope this helps. 

No they’ve not done that