The Fall of Khaiden-Sharnogg!

[Herobizkit]

if I (as a PC) were to suddenly find myself in command of 200k troops, you know what I'd do? I'd start assembling staff to monitor and take care of said army. Once that was done, I'd head off in search of loot/magic to support said army and 'check in' every so often. Most of the stuff you describe can be figured out and set into motion 'off the table', that is, figured out in between game sessions. Maybe that's just me... I have a solo player arranging something similar (minus the army) in our solo campaign, and my answer was to fast-forward a few years and move on from there.

If you have it, there was a lovely monthly/yearly random events chart in the old 1e Oriental Adventures that could help you fill in the blanks while the pc's were balancing their checkbook.

 

[JoeGKushner]

You can always take a page out of modern times.

The Sharnu wizards sound like they were a powerful force.

Perhaps the players can dole out positions of various importance to friends and allies in the rebuilding of that order with their own goals in mind.

This could include guilds that would need to handle paper, ink, tutors, bodyguards, special components, access to different spells, raiding the Sharnu libraries, and dealing with any left overs.

In terms of Khaiden-Sharnogg itself... depending on how much attention your players pay attention to modern politics, they could try to replace the entirety of the police force with their own soldiers or augment those forces while always on the lookout for those who might cause trouble.

Next up would be repelling any 'skrimish' forces that foreign governments claim to have no control over. Perhaps even going so far as to invade on those the weaker countries and even permanently station troops there. For example, the Hadrim barbarians look like they would be troublesome but their location might prove tactically useful. Since their independent, they probably wouldn't get any full support but under the table where others couldn't accuse them, foreign powers might supply weapons, training, access to summoned monsters, forged constructs, etc...