Panoramic city wip/commission/advice

[a.coldyham]

I have a great idea in my head (don't we all) for a map, laid out like a wall painting, of a siege which happened in my campaign world.
The last city of a great Drow civilization, already huge and swollen by refugees fleeing the combined human armies, is under siege.
The scene has a hilltop in the foreground, general's viewpoint sort of thing, with a bunch of arcanists. On the plains in front of the city armies clash, amongst flashes of magic. The city can be regular, but with a large number of religious buildings, focused around a huge cathedral in the centre.
The particularly unusual thing is a planar tear in the sky above the city, opened by the arcanists. One problem. A stray arrow hit the main guy, and magicians on both sides stop everything to focus on closing the rift above the oblivious armies below. In the end, they close it, but only after a large chunk of matter fell through, destroying the city. Only one building stood firm. The cathedral in the centre, sucking the life-force of the many souls bound to it within, remained, a shattered silhouette against the sunrise, the last survivor of such a fateful night.
I think I would like to do both views from the same place, one as the arrow hits, one as his body is shrouded and carried off, with the sea flooding the crater, washing around the cathedral.
I am aware city maps are some of the most difficult, even from conventional angles, but I don't want to lose the vision I have.

tl;dr, perspective city under siege with rift above, hill in foreground. Probably too much flavor text.