Miquella's reaction is less swift, but he rushes after Joran, and tries to protect them with an incantation. His first attempt fails to produce any effect. 

Deskari can only stay here for a few rounds after taunting Iomedae, so he positively welcomes mortals who rush into melee range.

Can he kill them in one round like he did Terendelev?

Unlikely, but he can probably do it in a couple. 

Can she get a slash in?

If she's the strongest human in the world and buffed by the best clerics, sure. Not like a hit or two from a sword is going to affect him.

Did she know that anyone hit by Deskari is poisoned and rapidly withers away? Oh, and is also infested with tiny demonic locust eggs? Those should be bursting out of Malenia's stomach in a fully-fledged demonic locust swarm and dealing a lot of damage in the process, right about - a second or two after he hit her, actually?

Her sword is

1) Large

2) Enchanted

3) Enchanted specifically to ward away any and all gods and adjacent beings, which probably includes outsiders

Did he know that she is already diseased and… rapidly… withers away. Been her whole life actually. And the locust eggs are better be good at surviving the rotting disease within her body, Miquella's vast array of protections isn't going to cover them. 

Meanwhile, he tries a different approach to casting, weaving the fundamentals of order with his own power into a disc of holy light, launching it at the closest demon. This time it works. 

Annoying. But he can still kill her the normal way next turn, right?

Since she's unusually powerful for a human, he'll even take her body back together with Terendelev's, it might prove useful.

At this point, someone in the crowd shoots Deskari with a crossbow bolt that, against all sense and sensibility, actually draws blood.

He can accept people committing suicide by him, but shooting him and daring to hurt him and then (probably) planning on running away? That, Deskari will not abide.

A little gnat snaps its jaws at the Lord of Locusts, he rumbles as he raises his giant scythe high overhead, Malenia momentarily forgotten.

The only nice thing about having to leave soon is not having to save any of his power for later.

A strike with all his might behind it opens a great fissure in the ground, a hundred feet deep at least. It splits the square in two and keeps going right on through the city, outpacing the refugees escaping the square and even their screams, the ground shaking and buildings crumbling in its wake.

Iomedae's cathedral collapses on itself like so much rubble.

The gnat that dared to shoot him is well and buried, now.

When Deskari is distracted, she attempts to get a few more hits in, but then she senses…

A fissure opens right beneath him. He's definitely falling down. 

She doesn’t admit defeat, but she's not going to abandon her brother. She backs off Deskari, and jumps down the fissure. 

Her body isn't worth chasing her for; he'd rather spend the turns he has left killing everyone in the square with a strong Lawful Good aura. Like you, Iomedaean, and that dwarf over there. He tagged them (mentally) while he was in the time stop, and they will not escape his swarmsight.

Not everyone here is immune to his poison, right? Have some acid poison spit, everyone who thought to make a stand together, and as many more as he can reach in a round of flying. His poison and his swarms will take care of any who survive his first hit, and the lesser demons will chase down the rest of the city after he's gone.

And then he teleports over to his real objective: the Kite, the two-story building housing the Wardstone. It is as well-warded as the hands and minds of mortals and angels could make it, in a hurry and on a tight budget.

Riftcarver laughs at the barriers between dimensions; the best wall on this sorry little planet could not keep him out.

Deskari grasps the Wardstone. It burns him, but he can sense the poison that weakens it from within, and he can stand its touch for the half-second he needs.

The Wardstone arcs over the city, a ridiculously massive gem shining with all the colors of the rainbow, and smashes down through the roof of another little fortress a quarter-mile away.

That landing probably squished some more paladins, but sadly Deskari has to depart before he can hear the sound of the crash.

He falls down the chasm opened by Deskari, not the most graceful fall, but not enough to noticeably damage him. Malenia jumps down near him, he takes her hand to reassure her that he's fine. 

Where are they now?

At the chasm's bottom! It's uneven but thankfully made out of solid earth and stone, and strewn with rubble. There's a slice of sky far overhead, obscured by dense dust. The ground trembles with little aftershakes, and the sounds of fighting and screaming filter down from the plaza above.

They can't see far along the chasm because it's not straight enough, but there are sounds coming from further ahead which are probably be voices.

She wants to leap out of that chasm, and continue the fight with the giant locust thing, but...

...somone might need their help, they're going towards the voices.

After a few turns they reach two more people. One has her leg pinned beneath a heavy rock, and the other is trying to help her.

"Fellow survivors, thank the Inheritor! Can you help me free her?"

Anevia isn't thrilled about trusting her life to strangers (who aren't paladins) but they look too powerful for Seelah to stop on her own, so she just smiles and says "please" in a pained voice.

She'll move the rocks, they aren't heavy for her.

Meanwhile, he'll talk to people.

"I'm Miquella, and this is my sister Malenia. Do you know what happened up there? It was all so quick..."

"Thank you! I think my leg might be broken..." She tries to stand up gingerly, leaning on Seelah.

"That was the demon lord Deskari. I've never heard of a demon lord appearing on the Prime Material! And the Wardstone should have stopped the other demons at least." She frowns. "I don't know why exactly demon lords don't attack directly, besides that they're probably afraid of dying. I... guess I hoped the gods wouldn't let him."

"Demon lords have never been seen in the Worldwound," Anevia confirms. "If he's still up there, only an archmage stands a chance and could respond in time. Some people in the city have sending spells and will definitely have started casting them, but they take ten minutes and I'm not sure the city can survive ten minutes of Deskari as a physical structure, never mind the people in it. Maybe someone can summon an archon that can teleport with a message."

These two look powerful, if only (in Miquella's case) by not looking at all ordinary, and are also unfamiliar to her, so Anevia assumes they're adventurers or crusaders or some such and have at least an approximate understanding of the levels of power involved.

"So let's hope very hard he's gone and we only have to deal with all the other demons. With the city in disarray, it will take some time to mount an effective response. A lot will depend on who died and can't be quickly resurrected, besides Terendelev. Everyone important was in that square, even Prelate Hulrun." By which she means he certainly wasn't there to enjoy himself, he spent the day working like always, it's just that everyone he wanted to interrogate or spy on went to the festival so Hulrun had to follow.

"It will also depend whatever's up with the Wardstone, since yes, normally it wouldn't let those demons get into the city. I saw some babaus before I fell, they're definitely not strong enough to do this on their own. Maybe Deskari found a way to really power them up." There's a cheery thought.