It is my understanding that the teeth can remineralize but cannot grow back. If that is true that means you can recover from a cavity because the cavity "hardens" but there will always be a "hole". Is this correct? If so, would you need a filling if you were able to stop the decay?
In the case the decay is stopped and there is no pain bothering you, it's not necessary to drill & fill the tooth. Conventional dentistry says that once the dentin is exposed the missing enamel won't grow back. Various advocates of alternate health claim otherwise. One claim I have heard is that under certain conditions the tooth can remineralize from inside out, meaning that first the damaged dentin is repaired and after that the surface enamel. I have not achieved anything beyond stopping the decay though.