That is just not a reasonable question.
The question should be, " How far will I have to drive to get an air fill?" And the answer for most of us, even if you just randomly eliminated half of the LDS is probably less the 10 miles more than you drive today. I'd like to see Darwin do his thing.
Why do you need an LDS?? Because they make it easy. Especially if you are unwilling to learn about gear and don't want to waste time shopping.
You may not think it's a reasonable questions but it's a valid question. Also appears you didn't read my entire post. If my LDS closes, I'd have to drive 16 more miles out of my way just to get fills. I consider myself a very consistent diver, I dive on average of twice a week. Those miles would add up quickly and most likely eat into my diving budget.
Most people/divers are fickle. If they have to drive more than a few minutes they will give up because it's not convenient any longer. We live in an instant gratification world now. If kids can't get what they want right away they look elsewhere. Where else is there to go if all the LDS's are closed because no one purchases gear from them any further? All this cause people want to save a couple bucks.
It's the equivalent of driving two miles past the first grocery store to save a nickel on a loaf of bread at one further away.