It's not speculation that he died at all. Think of it this way. In the BS of TP when we see Ganondorf get stabbed, he doesn't die. Why doesn't he die? It's becuase the ToP awakens within him. There is nothing in the game that confirms that's why he didn't die. The reason we know that the ToP is the reason he didn't die is because we see him seemingly die, then we see the emblem shine on his hand and he comes back to life.
At the end, when he gets stabbed it's the same thing except opposite. We see that he doesn't die right away, then we see the emblem on his hand go away and he just loses life. It doesn't need to be confirmed by text because it's very symbolical and clear that the ToP leaving his body signifies his death.
The Zelda series has never been 100% clear about the good majority of the things that we know are factual. Nintendo/Miyamoto/Aonuma like to be symbolic and epic and poetic when it comes to the Zelda series. There are lots of things that we don't need to be told about to know that they are true. Like the old saying goes, seeing isn't believing.