While I'm in uncharitable mood, it seemed that Negan's plan relied a lot on Maggie being severely ill and needing an ObGyn. Otherwise they might have just turned around at the first check point.
"checkpoint 3 come in, they turned around and went home"
"err we just spent a weeks worth of gas moving tree trunks into a wall, and poured another weeks worth of gas on it. Should we still set it on fire? "
And I understand how they might predict whuch roads they would take, but how could they predict that they would end up in that specific clearing, it's not like they guided them in any direction until the very end.