Then if he doesn't want to fight on the ground, he has no reason to complain about it. The ref will intervene to save him from having to fight where he's less secure.
Hall has no obligation to stand in front of Maynard. He knows what the referee is going to do when Maynard walks away. The decision comes from Maynard has to how he wants to continue the fight; not Hall.
So, yes, from a purely combat standpoint, Maynard does have an obligation, or he can't complain about Hall going to the ground. It's not against the rules, nor should it be. There is nothing to complain about.
As a fight fan, you should be upset with Maynard for refusing to fight on the ground. It's that simple. The ball was always in Maynard's court. Stop looking to the referee to make the fight the way you want it to be. Fight your opponent.