[They both had the same thought when they agreed to step inside the cockpits. Both willing to give their lives if it meant that they could achieve peace. Of course neither of them could let their friends die either.
Either way, they're stuck in this place now without any access to Sein or Nicht because what warden would give them such powerful weapons? Though he doesn't doubt for a minute that if they had the opportunity, they'd do it all again.
Soushi doesn't ask for a list of the names of the fallen. He may not get to experience it for himself but he seriously doubted that anything he learned here would come back with him when he finally left this place. Therefore he could do nothing to save anyone even if he had the information.
As for the idea of being reborn... he thinks back to Tsubaki and Orihime. It was very likely that he'd be the same way. A new person who may remember the life before - who remembered him as he is now.
What does someone even say to that? Apologizing is not the right thing to do even though he's once again left Kazuki behind. Nor is saying thank you for surely his friend is taking care of his reborn self.]
You'll be able to return to Tatsumiya Island soon. For now it seems we're stuck here in this prison.
[Meaning that they should focus on that a little more.]