After reading a recent mailbag, one person was asking why Mario and friends were spared after Sammer's Kingdom fell victim to The Void. After not finding the answer before asking, the person considered it a plot hole. I have found some evidence that it isn't a plot hole. I'm not 100% sure about this right now, but if you directly quote what Merlon and Nolrem said, it gives you a little of an idea:
Nolrem: "At the Duel of the Hundred, the hero will meet with dark powers of purest chaos. If you fall to the Hundred, the chaos world grows and the Purity Heart fades. And as that happens, the hero will fall to the world where all games are ended."
According to Nolrem, we can conclude that Mario and friends have a 100% chance of getting this pure heart, because if he gets the pure heart before Sammer's Kingdom collapses, then he is victorious. At the same time, if he fails, the Pure Heart in that area fades (loses power) and Mario goes to where all games are ended, also known as The Underwhere. With our knowledge of the games future, we know that Queen Jaydes brings Mario back to Flipside and restores the Pure Heart's power. Simply put in storyline terms: Mario will get the Pure Heart.
Merlon (before you go into the door leading to Sammer's Kingdom for the first time): "When seeking the Pure Hearts in a world on destruction's brink, perseverance is key."
Apparently, Mario and friends have to never give up if they want the Pure Heart. With in-game knowledge of what happens after you enter the door, we know that Mario and friends tried as hard as they can to get the Pure Heart, even if it seemed impossible. Apparently, according to the Light Prognosticus, it is foretold that the hero WILL survive if he has this trait.
We know that Mario failed and retrieved the faded Pure Heart, but how did he get to The Underwhere after that? We thought the Light Prognosticus foretold the hero going to "the world where all games are ended." Something happened to get them where they need to go. Dimentio comes in and sends them to The Underwhere. But, if Mario is dead, how does he save all the worlds? That's where putting this all together comes in:
Before Sammer's Kingdom gets destroyed, Mario and friends were trying their hardest to get the Pure Heart. With their perseverance, they were supposed to survive the destruction, and get their hands on the faded Pure Heart. Mario and friends needed to get to The Underwhere when they were still alive, so someone was foretold to send them there by different means; in our case, Dimentio coming in and sending them there. Still being alive and having the faded Pure Heart revived after all of his time in The Underwhere, Mario can now continue to save the universe.
I know all of this isn't completely accurate, but it clears up the confusion of it simply being stated as a plot hole. Any help would be appreciated.
And for the question by the same person about the marriage of Peach and Bowser, it doesn't exactly say that the marriage was canceled, but at the same time it didn't say it was official. I think they realized that the marriage was fake, and was held only to use the Chaos Heart's power.