Possible sandbox side story repercussion help

[Aurosman]

So, I am getting prepared for a future game where it will be a sadbox world, or close to one. The trouble I am having is how to think of reprocussion from ignoring a quest or something big.

I am looking at having the players encounter a strange town, where everything seems perfect and if they press further they find out about the miracle man in the town that everyone follows blindly, so basically a cult town(similar to the premise of Farcry 5 or Liore in Full Metal Alchemist) where most the members are ignorant to the true motives of the leader and a few others.

The two main question I am having are what kind of stuff would happen to the world if it was ignored and allowed to grow? And second, what kind of class would this leader and immediate followers be, thinking along the lines of priest, wizard, or some kind of illisionist for the leader and more melee/ranged for followers.

I know this is a sandbox game and I shouldn't stat out all the possible outcomes, but just some general ideas is what I am mainly looking for. I like to be a little prepared for whatever outcome would happen and can stat out everything if the time comes.

Any input is appreciated, thanks.

[InvisibleBison]

It's hard to say what would happen if the PCs ignore this guy without knowing his goals. If he just wants to be a cult leader with an entire town in his thrall, well, he's already got that, and he'll probably just stay around until something comes along and stops him. If he has larger goals of some sort, he will presumably do things to bring them about. If he's successful, he'll eventually draw attention from one or another powerful entities in the world, who will take action based on their opinion of him and his goals.

As for his class, thrallherd (http://www.d20srd.org/srd/psionic/prestigeClasses/thrallherd.htm) or beguiler are both good at mind-control stuff, but a wizard or sorcerer could do it as well. Most of his followers would probably be 1st level warriors or commoners, but with a few higher-level NPC classed characters and maybe a couple lieutenants with PC classes. If the leader is a caster-type, a melee-dude would be reasonable as his bodyguard, and it would make sense for him to have recruited another caster of a different sort with synergistic abilities.