Tisto stoops down to inspect the body of Calisto.  His recollection is partially correct.  She had a mask, not just the fragment of one.  The full Ainoe is still on her face. The mask is wrought from luminescent white stone.

With no one else around and the two remaining undead? minotaurs preparing to leave the temple unless you try to stop them, you find yourselves in possession of all of the fragments of the Elpis mask and also the Ainoe mask.  Calisto is dead and you are unsure how the gods may react.

"Well what do you know! Look what I found!" Tisto says to the others holding up both the remaining fragments of the Elpis mask and also the Ainoe mask "so now what?" he finishes with.

"In the end, we recovered the Ainoe mask and collected all the fragments of the Elpis mask. I think that the Gods, or at least some of them, will be pleased by our deed." says Areus. "Let's exit this place." The hoplite kneels down to take Callisto's body and starts walking towards the exit of the temple.

“Very well.” Saya looks at Calisto, and wished that she could have saved her. She tells herself that this was Calisto’s fate, and that it saves them the trouble of not having to fight her. Thought, deep inside, she has doubts, and try not to think too much of the implications of her death. She follows her companions out of the temple.

Tisto, make a Cha saving throw DC13

Soren growls "We made an oath, and despite it being broken by actions that are not our own, that oath has been broken. We are in the underworld, for Thassa's sake, could we not find her soul and reunite it with her body?" 

"Well good to know we'll be suffering the wrath of a god," Callaphe says, though she doesnt look to upset.

Tisto, make a Cha saving throw DC13

Tisto's saving throw = 14 in case it is a magical effect he is saving against here is the second roll for Advantage 19 

Tisto touches the cold stone of the Ainoe mask and holds it up.  Nothing happens as he does so.

"She died here, but I do not see her soul nearby. Maybe one of the Gods already claimed her soul for a different purpose." replies Areus. "Anyway, we should exit this temple and attempt to find a way back to the world of the living."

“I ageee with Areus. Even if we did find her soul in the Underdark, or anywhere else for that matter, I am not sure that we would be able to anything to help her.” Says Saya, ready to leave the temple.

Tisto holds up the mask and the fragments - examining them both as he does  "well if nobody else wants these I guess I'd better carry them" as puts them safely in his backpack.

Quote from GrantFromCanberra >>

Tisto holds up the mask and the fragments - examining them both as he does  "well if nobody else wants these I guess I'd better carry them" as puts them safely in his backpack.

 As a point of clarification Tisto has the Ainoe mask and the Blue Fragment.  The others have the remaining fragments spilt among them.

As Areus picks up the body of Calisto her battle axe clatters to the floor.  You look back at the others, Eftalia's spear lays on the ground next to her body.

The minotaurs slipped away while you were discussing things and are no where to be seen but you soon find them.

You make your way back through the temple and find the path you took underground.  As you get close to the point where Kunoros was you hear the clash of arms and hear the minotaur battlecries.  

Areus before leaving the temple takes Eftalia's spear "It may still be of some use to us."

"It looks like that we have found the minotaurs." says Areus as he hears their battlecries "Be prepared as I fear that they are battling the guardian we passed before."

(Can Saya have Eftalia’s spear?)

Saya gets ready for combat.

Areus picks up Eftalia's golden spear.  He immediately notes its exceptional quality. 

Areus offers to Saya the spear "Take it, I already have one." The Akroan, spear and shield at the ready, carefully walks towards the sounds of battle.

"Thank you." Saya replies to Areus. She puts away her battleaxe, and wield Eftalia's golden spear.

You step into a room that you had passed through earlier and at the far end you see one of the minotaur already on the ground, presumably dead considering the bite and claw marks on it.  You arrive just in time to see Kunoros breath flame onto the other minotaur as it writhes in pain and falls to the ground. 

Kunoros looks up at the group as you approach.  "And what are the rest of you doing here?  I can smell a lie a mile a way, so do not lie to me as these fools have done."

"The Gods sent us here to retrieve an item of particular importance. Now we are on our way back to Theros." says Areus still holding on his shield arm Calisto "We have no quarrel with you, let us pass."