This wouldn't be possible but hear me out (Sariel & Tarmiel) Part 1

                                    

                                          
Okay, if we assume one of them survived Mael and the Meli Demon King fight (which would be impossible, but please just play along with me) how would it look like for them emotionally, I'm just gonna write my guessed and you guys can add some stuff if you want to. 
Tarmiel survives
When Sariel died in his Arms Tarmiel tried to yell something to Mael in frustration to please remember the kind person he used to be (didn't work ofc) 
He was able to dodge the attack that was supposed to kill him somehow and ran towards the others. Elizabeth glad that he managed to escape the attack, but then saw Sariel who was still in Tarmiel's arms. 
Before she was able to say anything else, Tarmiel started to cry more than he already was, apologizing over and over saying that he was sorry that he wasn't able to protect her, to save Mael and for being the reason his best friend was now dead. 
Gowther then stepped forward asking Hawk if he could take care of King. Mael then starts an another attack before Oslo and Diane arrive. 
Gowther showed her what has happened and she's shocked about it of course. 
Right after that Mael transformed into that state. Everyone looks at him with shock and fear. 
Tarmiel was only able to look at that form that was Mael, that he was in a way responsible came to existence. 
The fight I would say went as it was in the series, but with Tarmiel helping Elizabeth with the healing and helping as much as he was able to while trying to protect her as well. 
After the Island was destroyed he had to fly in order not to fall into his death, he looked around for the others, he saw the corpses of Oslo and Derieri falling down but continued looking for Elizabeth, the others and Mael. 
He saw Elizabeth and Diane and flew straight to them. 
Elizabeth was glad that he was okay but was busy trying to save Diane. 
When both he and Diane saw Mael they tried to warn her but King came just in time saving Elizabeth and keeping all of them save with Pollen Garden. 
The fight then went on as usual. With Gowther entering Mael's mind and telling him the truth. The real Mael came back saving Gowther. Tarmiel just like Elizabeth were only able to cry tears of joy. Tarmiel spoke to Sariel, who was still in his Arms, 'Mael is save, so is Lady Elizabeth Sariel'
He added in his mind 'It wasn't your fault, it was mine. You deserve to be an Archangel the most out of both of us'
Tarmiel went straight to Mael after they reached the ground, Mael wasn't really able to look at Tarmiel in shame of himself.
'Tarmiel i-'
He wasn't able to finish because Tarmiel gave Mael a hug with one arm while the other still held Sariel. 
'Im so glad that you're back Mael. How are you-'
'I'm so sorry Tarmiel, I'm so sorry!'
'Mael... It's alright you don't need to apologize f-'
'I said awful things to you! 
I killed Sariel I'm sorry!'
'....Mael'
'I'm not begging for forgiveness, I would be even more grateful if you were mad at me for what I did more than you forgiving me...'
'I can't be mad at you, because it's my fault that you turned into that state'
'.....pardon me,I need to do something first'
Mael put a spell on Deriei and Oslo for them to hey reborn with their memories. 
'If they ever seek revenge on me, I'd accept it's
'If yes me to'
'Gowther... '
'Mael, please come with us to Camelot if we want to win this fight we need your help'
'Me fighting for the Goddesses against the demon's...Who would want such a thing? My brother? Sariel? Or all the other commarades I killed-'
'I would-'
'I'd wish for that! Please help us fighting Mael!'
'You heard her Mael'
'Also Tarmiel, what are you going to do about Sariel?'
'I.... I'll get rid of him myself don't worry...'
'You sure you can?'
'Yes... Lady Elizabeth...'
Tarmiel put a similar spell that Mael used on Sariel which just made his body disappear into light particles. 
He cried a bit while doing that asking Sariel for forgiveness and wishing him farewell till they see each other again. 
I'm skipping that whole Demon King fighting battle now... Maybe if I have more motivation. 
But the thing I would say is that Ludociel would also after he talked to Mael go to Tarmiel and ask him if he is okay (he knows about Sariel) until the Demon King gets revealed. 
When Ludociel was sacrificing himself saying the line of him wanting never to lose anyone who is important to him again, Tarmiel was a bit shocked to hear that from him. He knew that Ludociel had a soft spot but never would he have imagined him saying that so directly. 
When Ludociel died in Mael's arms, he started crying a little again, also telling Ludociel a few words that bought a smile to his face before he also turned into light particles. 
(Maybe if I'm motivated enough I'm gonna write that a bit longer and continue.) 
I'll try to drop part 2 soon this week as well I hope you guys kind of enjoyed it 😭