Well, I think Quentin had the highest initiative roll, if I remember correctly, so his spell hits the six quasits before Raven gets there:

Saves: 9  7  9  15  17  14

Four quasits die in Quentin's fire blast!

Quasit save: 15  Was -1 on first roll: looks like you can still mess up the dice by adding more rolls in front of them. Yep, re-rolling every time I edit now. Sorry about that, you will have to take my word for the first responses.

Del casts Mind Sliver at a quasit and its little head explodes!

Raven slices and dices the fifth into bits.

Starting fresh: the six hallway quasits are toast.  (Raven got the sixth.)

Wizards and Mindartis hurry into the hallway, a few of them taking AOO attacks. 

 Three wizards are down!

Mindartis grabs one of the downed wizards and starts dragging him out of the room, rage subsiding.

Elwin also rushed out of the room as the fireballs began, ignoring enemy swipes. He turned back to examine the situation.

(( That's his only activity, since there are no quasits left outside. ))

(( Have they stopped fireballing the room? ))

 A couple of wizards cast Dimension Door to pull out the fallen and Mindartis as fireballs blast the far end of the room, and then Lonvari finishes off the surviving quasits rushing the open door to the hallway with Thunderwave.

As the ashes begin to settle over the now-quiet room, Mothander says, "Well, I suppose we must rethink proofing our circle against being broken by dropped items, and possibly add a few more layers of doors and other security measures to the lab. And perhaps a door guardian."

"Where is the jackanapes who started this?" Lonvari bellows. "I will see the rascal SUSPENDED! Preferably by the toes, over a vat of centipedes!"  The gnome demon-summoner is not among the group, though, and it seems likely they turned invisible at the beginning of the battle and ran away.

"Why were you summoning demons in the first place?" Mindartis asks through gritted teeth.

Del will go up to one of the downed Wizards to try to stabilize Medicine 11 while bonus action casting Healing Word on another 8 hit points restored - He's singing appropriately he makes sadness - disappear - demons worry - when the wizard is near ...

“I don’t think the student was meant to be summoning demons. At least not powerful ones. With the proper precautions they won’t be able to do anything but this student seemed not to take the proper steps.” Quentin answers Mindartis some 

"How are you doing prince?"  Raven asks the prince who is looking a bit worse-for the wear. She moves to any of the downed wizards,not yet healed and gives them 1 hp of healing per her paladin lay-on-hands ability.

"Thank you, Quentin," says Mothander. "We summon for the purposes of education and research, of course. But students are supposed to seek approval and sign up before using the rooms, and overall, have supervision before summoning anything, and we certainly would NOT have approved the summoning of such a powerful creature as this without several staff members standing by in case things went wrong."

"I am well enough," says Prince Lintelér, in spite of looking pretty beat up and sick. "Thank you. And you?"

At Raven's words, the wizards remember who they have in their midst, and huddle around the prince, casting healing and restoration spells--probably far more than he actually needs--and apologizing profusely. They attend to the rest of you as well, and thank Del very much for his assistance.

(You are all healed up and un-poisoned)

"Well," the prince says eventually, "I'm afraid we've overstayed our planned schedule, and must be getting on now. I thank you very much for your kind hospitality--"

"Oh, we could not dream of you going on now!" says the Chancellor with horror. "You are all exhausted. You absolutely must rest here for the night! Let us make amends for what you've been through!"

They argue politely back and forth. Eventually, the Prince takes you all aside and says, "I was meant to smooth over our relations with the Simuls and the Naicas as I passed through. If we leave now, I worry that the Simuls will believe it is because of this incident and that I am offended. If we are to spend tonight at the Naica's tavern, we should go now. If we spend a night here, it will mean that we go there tomorrow and will arrive in the morning. I am not sure I can stay diplomatic if i am forced to spend all day long socializing with the Naicas. They think of little but drinking and gambling, neither of which I enjoy. Do you feel the need to rest here tonight? Or can you think of a diplomatic way out of this?"

I would think that having to  alter your schedule Del suggests would imply that the incident was a major occurrence. "Though surprising" one might suggest "quick action by the staff kept conditions under control" is a better narrative than "we could not control our students and so the prince had to miss his meeting due to wild demons everywhere". 

“I agree with Del, as much as I’d rather spend the night here if we’re trying to smooth over relationships we shouldn’t be late for predetermined meetings. Perhaps declining saying that you cannot miss your meeting the Nacias as they have already cleared tables and a room for you and it would be rude to do so. Before we leave though we should double check for a certain stowaway.” Quentin suggests 

Mindartis nods, "Push comes to shove we can just slip away in the middle of the night."

The prince seems cheered up by your advice. Returning to the wizards, he tells the Chancellor, "I will be certain to speak of how bravely, quickly and competently the Simuls deal with an unexpected enemy. I pity the gnoll raider who dares set foot on your campus! But I am expected elsewhere, and we wouldn't want to blow this unfortunate but minor incident out of proportion."

It takes a while for the staff to be totally convinced, but soon they call to have your horses and carriage readied for your journey.

Del soon finds himself cornered by the Bardic Studies students, demanding details of the fight, and occasionally crying out, "I can't believe you didn't send for us!"

Life moves pretty fast. If you don't stop and look around once in a while you could miss it. Del quotes one of the great wise ones.  'Sides, you can write a better story not knowing all the facts. The ah, perpetrator - a gnome in black I heard - disappeared. You could find out who it was and why and all. Do a little of your own investigating. I'll let you know what I am up to, but you gotta allow some time. Six days I'm in this country and you tell me I'm not letting you know stuff fast enough.

Del pushes off the students and gets on the way, singing a travel song

Being cautious Quentin will thoroughly attempt to check the stables and such to make sure a certain Nacia hasn’t stow awayed on the carriage, even going so far to ritual cast Detect Magic and make sure he isn’t invisible. 

Investigation: 11

Raven gives the help action in this investigation effort.

The help advantage roll (includes the modifier in the roll): 26

You find no hidden Naicas or any other stowaways, though the Detect Magic spell does make the prince's sword and shield glow nicely.

(If you are all ready) Soon you are mounted up again, the children in the coach demanding to know what happened and complaining bitterly that Hogthimble did not let them go and watch the fight.  The prince rides his horse this time (Possibly to look more dramatic, as urged earlier, possible because riding was a slightly more peaceful way to pass the journey than being cooped up with the kids.) Students cheer as you ride off! Now in addition to 'Mole-whackers!" many students are cheering you as the "Demonslayers!" and the "Protectors of Lomalos!"

But the Bardic students do not sing of your latest triumph yet--while they all agree that Quasit rhymes with 'What the heck was it?" a bitter argument has started about what rhymes adequately with Nalfeshnee.  The ballad of today's fight might take a while to prepare...

Once you've passed out of Simul territory, and the cheering students have been left behind, Prince Lintelér says, "I don't know what my father offered you for this task, but I'm quite certain that fighting demons was not in the job description. I will see that you are appropriately compensated."

"it's no worries," Mindartis laughs, "I've always enjoyed a good fight."