Well, I would say at least try to drive him off by doing enough damage to him.

AREA 15 to 20

Like the caverns above it, Arauthator’s lair is composed entirely of ice. The rough ceiling of the open cavern rises 40 feet above the varying height of the uneven floor. The floor of the cavern is worn smooth and is highly slippery. Maccath has makeshift cleats to allowing walking on the ice easier. The terrain levels represented on the map of the cavern show increments of 8 feet. The elevation of the floor results from the ice splitting and splintering, so the ledges are abrupt and have a distinctly step-like appearance. 

The lair cavern is dark. Maccath casts light to illuminate the area. The lair cavern is colder than the tunnels and chambers above it. The cavern is a bone-chilling 0 degrees Fahrenheit. Area 20 is even colder. Banks of vapor roll through the cavern, limiting visibility to 60 feet for characters with light.

"YOU HAVE FOUND THE HORNED ONE, BUT SHE IS MINE. THE END IS NEAR. SOON, YOU SHALL SEE THE FINAL FACE OF YOUR DOOM. DO NOT DESPAIR, SURELY, OBLIVION IS PREFERABLE TO YOUR POINTLESS LIVES."

Pillars and platforms of ice jut up from the floor in this area of the cavern. A jagged ridge of ice divides the cavern into sections. As you slowly approach area 19, you can see a large pile of treasure on the ledge. The western end of the lair cavern is where Arauthator currently grips at the ice, ready for you. Gold, jewels, and other treasure lies scattered on the floor and frozen into the walls of this vast chamber. Pools of slush spread across the floor of the cavern, prevented from freezing by the seawater’s high salt content.

He is easily the largest dragon, white or not, you have ever laid eyes on to this day.

It is noticeably colder here than anywhere else in the iceberg, reaching –10 degrees Fahrenheit. Everyone needs to make two saving throws. The first one is a DC10 CON save or suffer one level of exhaustion. The other saving throw is a DC14 WIS save upon seeing Arauthator and not become frightened. (NOTE: It's difficult in real life to convey to you guys in words the sight of something truly monstrous as the presence of an ancient dragon, but rest assured your characters would be very nervous or anxious at this point. He is so large and menacing try to imagine how your characters would feel at this very moment in the darkened ice chamber of encountering and engaging such a dangerous creature.)

Con: 11

Wisdom: 16

Messalina had survived a lot, but admittedly the prospect of dueling a dragon did not appeal to her. Even as she inspired Li'riya, her words shook a little.

DC10 CON: 12

DC14 WIS: 12

OOC: Meh. Astrid is used to every other creature towering over her, so this is no different. 

Con save: 18

Wisdom save: 27

Although a dragon had been the one to take everything away from little Bell, when her eyes met with the gargantuan creature, she showed no fear. She was ready to take down one of the most fearsome monsters in the land at seven years old with her new found family right beside her.

DC10 CON save: 18
DC14 WIS save: 8

Upon seeing the sheer size of the dragon through the darkness, Camilla began to get very afraid and stared backing away, leaning on an ice pillar and hugging it tightly, trying to hide behind it. Shaking her head "No" rapidly, she began to sink to the floor, breathing fast, curling up.

"****************! I can't I can't I can't I can't..!"

Astrid to Camilla: "There there, young one.  Have no fear!  No worries!  That's not a dragon....it's a drag queen!"

Deception: 8

Li'riya moves across the ice effortlessly, accustomed to difficult terrain.

Con: 19

Wis: 19

Ka'ralya also has little issue with the ice, and designates the big nasty as her Slayer's Prey.

Con: 21

Wis: 14+1

Li'riya's hands shake as she nocks an arrow, the massive dragon impressing on her just what they're trying to do. Ka'ralya gives her granddaughter a glare. "Get it together. Remember, we fight so others don't have to." Li'riya takes a deep breath and nods, hands steadying, although her eyes are still wide. Ka'ralya seems unaffected by the massive dragon, her experience lending her some help against the creature's sheer intimidation.

Im not even gonna roll an insight check for that.

”A drag queen?? Really??” Camilla spat out. “******* hell! That’s your comforting advice??”

(Initiative will be rolled shortly.) Here is the current position map: (S = Messa)

Messalina looks at the rest of the group. "Don't clump together and make it easy for him to get us all. Split up!"

Con ST: 10

Wis ST: 20

”My love loves you. But I must slay you.” Edward says as he gets his katana ready while Fred hides in fear. Edward being the idiot he is moves forward towards where he things the dragon is. 

Initiative: 17

Initiative Li'riya: 5

Initiative Ka'ralya: 15

AAAAAAAAAAAAAAAA: 18

Fun Time For Everyone: 21

Arauthator: 16
Camilla: 11

Bell18, Messa17, Arauthator, Camilla11, Li'riya10, Ka'ralya8, Edward3

Astrid: ?????

Messalina will use Cutting Words to take 5 off of Arauthator's Initiative roll. 

Updated initiative order:

Bell18, Messa17, Camilla11, Arauthator11, Li'riya10, Ka'ralya8, Edward3

With a mighty, deafening roar, Arauthator sees you all engage, the very walls of the cavern shaking.

"Oh god oh god oh god!!" Camilla yells, covering her ears.

"YOUR TRAGEDY SHALL BE WRITTEN BY MY HAND!"

Messalina sends a Fireball at the dragon and also takes a moment to inspire Edward.

"If you get killed by that dragon, I'll write a song about you."

32 fire damage. DC17 Dex Save for half.