After you stretch your earlobes can they go back to their original size?

It all depends on a large area of factors: how your lobes are formed (big or small, thick or thin), how big you stretch, how fast you stretch (making sure you dont go too fast), how well you look after them (rubbing oils on them)..etc..

"the point of no return" depends from person to person, but if you do it extremely slowly and properly meaning only going up 2mm at a time and leaving at least 3 weeks recommended: 1 month) in between each stretch, as well as oiling up your lobes to keep them thick and healthy, then they should go back to normal-ish, up to 10mm. Any further than that will mean that they will never go back to normal unless you get an operation.