I don't mean to pile on, but most ATO's also have a maximum run time so this type of thing doesn't happen. If set up correctly the most water a system will lose is whatever amount is in the return chamber + maximum ATO run time. You'll burn up your return pump, but who cares. I guess if the leak is slow enough that the ATO can refill completely and resets every time, there's nothing you can do about that. In hindsight this stuff if always easily solved of course.
Really a crummy situation for you
. I hope some stuff pulls through.