If I gauge my second lobe piercings, how likely is it that it will grow back when i want it to?

First of all, it's called STRETCHING. A "gauge" is a size measurement.

Now, usually, a 0g or 2g is considered "the point of no return", however everyone's body is different. There are many other factors, like how long you've had them, if you've taken good care of them, and most importantly if they were stretched correctly and healthily (didn't skip sizes, waited proper time between stretches, used proper materials, etc)

Generally speaking, however, the 4g or 6g should almost definitely close up no problem, and the 0g should probably close to a normal 18g size, or pretty close to it (maybe a 12 or 14g, at most)

Once you gauge your ears, I think its a permanent thing, that hole is never going to just close up and go back to normal...