A functioning dick is dependent on the health of your HPTA and hormonal balance. Some will end up with lessor function, some will bounce back to normal. This is genetic.
There is the option of TRT if your HPTA is screwed up beyond repair.
That depends on multiple factors like your knowledge and experience in training and diet, the speed and degree of restoration to your HPTA and whether you've exceeded your genetic potential.
There's no such thing as a half natty. Small doses worth taking will still suppress your HPTA and replace your natural production of testosterone. This isn't Blade. There are no Daywalkers.