I realize everyone's body is different, but I'm asking in general.
in general the "no turning back" point is anything beyond a size 0. after that stretching becomes more than pushing the next size taper through your ear. But depending on your skin and how well it "bounces back" is how far you are willing to go. with any stretching there is always a chance that it will not go back down and would require surgery which is not less than a few grand. I used to have 0 size gauges and they closed almost all the way, but there are some signs of stretching still. if you ask some people, they would say that stretching is a way of life, depends on what your end goal is for your gauge is.
It varies from person to person. It also depends upon how large the gauge holes are and how quickly you stretched them. If it was done slower there is a better chance of healing. Options are to remove gauges, gauge down gradually or surgery.