The bubbling liquid at the bottom of the cocoon was what came after the heat rose until his body melted. So, it was undoubtedly hot. If Toz's guess was wrong, and he wasn't supposed to dive into the liquid with his consciousness and reform his body, it was very likely that he would perish. His clone would disintegrate fully, and his consciousness would disperse. There wouldn't be any hope of ever coming back to life and playing with the cats again.
However, when Toz made a decision inspired by his relative insanity, he knew better than to think too deeply about it. It would be better for his mental well-being if he stopped questioning each and every one of his decisions.
Besides, diving into the bubbling liquid with his clone would only change when he died. Toz didn't think he would last long enough in the outside world to find a vessel he could haunt. And if he was going to die anyways, it would be better to go through with the option most likely to succeed in saving his life.
