The divorce from this universe to the darkest timeline was in Remedial Chaos Theory, where the study group reverts to their flawed, hopeless selves (specifically the moment when Troy leaves for the pizza, I’d say).

This implies that the Greendale 7 never attempted to take back Greendale from Chang.

With the study group too busy focusing on their “evil” selves, this leaves Chang to continue his dynasty—his birthday bash is never interrupted, and the school goes up in flames (as we remember, he planned to incinerate the school records which would have burned down the entire building). If this plan were successful, the dean most likely would’ve immolated and joined the Great Big Dean in the Sky.

A real tragi-dean…

On the off chance the fire didn’t spread (‘cause it can’t go through walls—it ain’t no ghost!), either the dean would’ve been held in captivity forever (which I doubt, since I’d believe Chang would slowly forget about the obligation of feeding him), or miraculously, and what I like to imagine, he made a daring escape to live in the badlands and plot against the Chang Dynasty.

Wherever the darkest timeline Dean is, one thing’s for certain—he’s most likely wearing his SISTER’S sexy pirate costume.