If all you want is to keep it going, you don't need to harvest at all. Left in the ground, the garlic will continue to grow and multiply as clumps, becoming so dense that it chokes out weeds on its own.
I had that happen. One year I had some health problems and couldn't keep the garlic patch weeded. When harvest time came, the weeds were so thick and my stamina so limited, that I just wrote the patch off as a lost cause.
About 3 years later, I decided that section would work well as an apple/berry patch. The weeds around the perimeter were tall enough that I had assumed the entire area would need reclaimed. To my astonishment, the weeds around the perimeter were the only weeds that survived. The rest of the area was covered in a thick carpet of garlic plants! The bulbs themselves were so small they looked like scallions, but the plants didn't seem to care. I dug up part of a clump to use as green garlic, but left the rest alone. Later that year they formed so many scapes that I was able to use scapes in place of normal garlic all year long!
Last fall I decided to do this deliberately. I planted garlic under some berry bushes and fruit trees I had just planted, with no intention of digging the garlic up. I'm hoping it fills in the space and supplies lots of garlic scapes, while otherwise tending itself. I call it "feral garlic".
So, if harvesting is going to be too much of a burden and you just want the garlic to survive, feel free to leave it alone. Chances are, it'll do just fine.