That particular chicken will never get the symptoms again though, right? And she won't die from it. That's what I meant by "cure". Sorry, bad choice of words.
No. That particular chicken, if she does have MG (Mycoplasma Gallisepticum) could very well become symptomatic again and again, you just don't know. She may never show any symptoms again either. Can't say whether she would die from it or not either.
While the mortality rate from MG is fairly low in adult chickens, MG can often be accompanied by other respiratory viruses or E.Coli.
Stress can make birds become symptomatic (molting, integration/flock disruptions, weather changes, another illness, etc.) again.
Even if they never show symptoms again, they are carriers, this means they can spread it through dander/dust, feathers, droppings, etc. Any birds that have been living with them or exposed would also be considered carriers, even if they never show any symptoms.
Antibiotics will help with recovery and treatment of symptoms, but they are not a cure.
MG is also one of the few respiratory diseases that is transmitted horizontally and vertically. Horizontal transmission is bird to bird, dust/dander, your clothes/shoes!, from rodents, wild birds, etc. Vertical transmission is through the egg to the embryo in hatching eggs (very possible for chicks to hatch out as carriers of MG).
MG can also cause stunting/unthriftiness, also impacts egg productivity, can damage the reproductive system (it's been linked to Salpingitis in laying hens).