Nico was in the Hades cabin, thinking of his wonderful boyfriend, that he knew he'd never see again. Nico knew no mortal could find the doors of death and open them.
It
Was
Impossible.
And no hate to Will or Leo, but Nico knew they weren't very strong together. They wouldn't be able to fight well together. Will was specialized in healing, Leo was specialized is building.
And even though Leo can fight, the only weapon that he was said to have is a singular dagger. He had left his belt in Bunker 9.
Nico sobbed into his pillow, he wasn't satisfied at all with his last words to Will. He didn't go to say goodbye to the group as everyone else had. And he hated himself for it.
He hated the fact that the last words he'd ever had spoken to Will were "Get lost". Because Nico would never have guessed that Will actually would have gotten lost. In Tartarus too.
Jason was a completely different story. He trusted in Leo to try his best to get the two out, he knew that whatever damage happened to his boyfriend that the blonde doctor he had with him would be able to help Leo.
Jason was just anxious. He was waiting for someone to say that they somehow got in connection with the two, that they were safe! But alas, nothing.
Percy on the other hand, had completely shut out everyone and was currently locked in his cabin with Annabeth outside.
He could have saved them. It he had moved quicker he could've grabbed Leo's hand, arm even. But it had been too late.
Percy 100% blamed himself. It was obvious to anyone. Annabeth was worried sick. She was sitting right outside the cabin door, begging Percy to just let her in. (just let me iiiiiin) But Percy refused to talk to anyone.
He felt like he owed Nico and Jason. He thought they'd be furious with him, when neither of them actually were.
Clarisse was trying her best to try and communicate with Leo and Will, she was trying anything, possible or not. But her efforts weren't successful, she knew that she could've gotten there too.
She saw them. But she, like Percy, hadn't been quick enough. She had no doubt that if Leo and Will didn't make it back that it'd be partly her fault.
But little did they all know, Leo and Will didn't/wouldn't blame any of them.