Ngl this is kinda pushing into necrobump territory 
Nonetheless I’m personally interested so I would say… war. I’m serious. I sincerely think this was the best possible plotline:
I think this should’ve been expanded upon and made into the full plotline.
I also think that the map was kinda bad, although it wouldn’t really be Magius anymore here was my headcanon map made shortly before TGR was announced.
Magic making would be absolutely revamped. More customization is a necessary thing.
What I would do is throw in a skill system like the one I suggested here as well as introduce one of the several systems inferno made, with modifications. I would also throw in the Lost Spells.
Weapon revamp is necessary.
I would change the time period. Rather than Magius losing everything the AG was on the verge of, I suggest an almost industrial time period, with overall steampunk atmosphere. Airships, floating islands, etc. Weaponry should be greatly advanced.
Lastly I suggest mixing the diverse randomly spawning NPCs with fixed, AA style NPCs.