Madara, injured and dying looks up at the sky while thinking about Hashirama's words, the words that most likely will be the last thing he will ever hear.
Not that Madara regrets Hashirama's annoying voice being the last thing he hears, but he may have preferred not to have the annoying Senju be right there next to him as he died. Hashirama's words echo through him, and he can't help but keep thinking about them as his life force slips away from him.
Right now, we can drink together as war buddies.
The words stay in his mind, echoing through him as Madara starts to close his eyes, slightly taking in Hashirama's calm smile. It helps him slightly, even though he would never admit it. "War buddies, huh?..." Madara says, his eyes nearly closed. "I guess... That's okay..." His eyes close, Hashirama noting that even with the current circumstances he dies with a smile on his face. A slight one, but a smile none the less. Madara sees the darkness take him, and he takes it with slight relief.
He can see his little brother again. So he takes death warmly, and so everything is pitch.