The only possibility left is that what we saw was their afterlife. Yet, in the scene where they are lying on the stair steps, you can see both the bruise and the belt, which means Sora wasn't hallucinating either. Sora, on the other hand, didn't notice Haruka's bruise on his left knee, or the barely visible belt he was wearing, since she only turned around for a mere second before turning her back to him and running towards the centre of the lake. After all, Haruka, while chasing after Sora, didn't have a chance to see the stair steps atop which he would have been lying afterwards with Sora, which means he wouldn't have been able to hallucinate being on them in the first place. Haruka and Sora surviving couldn't have been a dying hallucination either. Which also proves that, while she was indeed the shrine's caretaker, she didn't find any corpses in the lake, despite being the only person who could've found them, since she lived there. She was the one who asked Kazuha whether there were other messages, which means she genuinely believed the text to be true and the twins to be alive. Also, Akira couldn't have been the one to send it. The torn bunny could have easily been replaced with a new one and Kazuha's message being a fake doesn't actually prove they died. Either way, it's irrelevant the hits of them being 'dead' aren't strong enough to be considered proof. You are either very good at searching, or you just lied about it (pardon my scepticism ). I have no idea where you found that information regarding the bunny being an editor's mistake.

Despite the overall darker tone the anime takes, the intention wasn't to kill the twins or imply that the twins died, and just came down to a mistake and lack of context The rabbit was confirmed to be an editors mistake, and, thanks to a scene being curiously cut from the anime, we never find out that Sora is in fact a great swimmer, and saved Haru's life from drowning when he was accidentally pushed into a swimming pool, and due to shorter dialogue after the lake, Haru never asks how they got out (she pulled him out with a renewed will to live after he asked for her to help him while drowning).As of December 2019, My Anime List user Kembobo was able to prove the twins are alive through evidence and logic on the poll 'Are Haru and Sora alive?'.Guess that puts the death theory to rest. Seems like with enough support we might be getting a sequel OVA for Sora's arc about how their life is continuing in their new city.

Yosuga no sora game english