Most moms will keep producing a small amount of milk with once a day stimulation. But for most children nursing only once a day, it's probably as much about the routine, comfort, closeness as it is about the milk. My twins nursed for 5 1/2 and 6+ years; by the end, I could barely express any milk, but my son insisted he still got some. If he got more than a handful of drops, I'd be surprised. But clearly my body kept producing a tiny amount. And some children don't really seem to care, and will continue nursing even if mom is producing nothing.
Some women will still produce small amounts of milk months after completely weaning. It just depends on your body and how much stimulation your nipples get (if you try and express milk a lot, you're stimulating some production, just really really low amounts).
