I personally love all the ideas, but the last one piques my interest the most.
There's a couple of ideas I am considering for that specific one that I listed below.
The standard 'kill the final boss' will not save the world, but instead accelerate the death of the world.
There will be an ending that will involve you having completed all the personal sidequests of every recruitable character and having them all survive to the final boss, wherein you use a command to attack one of them, then switch sides wherein you have to kill all of them, with another one of the characters spawning in to replace the dead ones after the prior's final words. To make it worse, this ending will be where the world will last the longest.
An early quest will have you assist a sibling to a local lord (who when you meet him is trapped in a dungeon) seize power from his brother, using assistance from a local rebel faction that wants him in control. Coming back later will reveal the old lord was a relatively benevolent individual compared to other individuals you would later meet, while the one you helped was a cruel and ruthless dictator.
The Emperor, who ascended to the position as a war hero, would have been dealing in sacrificing of prisoners according to dark cult rituals, nuking his favor with the populace, due to desperately trying to achieve the second ending I mentioned earlier. Near the end he would turn to wholesale slaughter of the capital due to how little time is left and how much he needs to do to achieve it.
My preference is number one.
Any specific industries you want to see in it, if that one is chosen?
I've been doing something similar to that in my game, actually. Basically, magic runs on a "Geothaumic Field", which the planet generates actively, and which is drained by use. For most of the setting's history, it remained at quite a high and useful level of energy, then something powerful started using all of it and basically cut the use of magic in the setting to a very low level.
In effect, any given area has a limited amount of power available in any period of time, and any magic use cuts into it, whoever uses the magic. Basically everybody shares one mana pool, so some players might, if they expect to face an enemy with an arcane advantage, intentionally use large quantities of power to run out the power supply and stop the enemy being able to use magic against them.
That said, my actual thought for this setting was something along the lines of A, the character dealing with the consequences of being so much more powerful that they render the large numbers of mooks most characters get a fair-ish fight against irrelevant, leaving them to handle having slaughtered mass numbers of people who couldn't harm them, and then getting put in situations where their capabilities aren't actually of any use. Diplomatic situations or famines, say.