Three Endings Are Better Than One
Okay, so there are actually three endings to this novel—which is something that hardly ever happens outside of a Choose-Your-Own-Adventure story.
However, maybe it's fitting for the game-within-a-game structure of the book. Untying such a complicated concoction takes more than just one neat little ending, right?
In Ending #1, Turtle solves the mystery, and the other characters go about their lives. She's the winner but no one else knows it. While this might not seem like much of a prize—apart from the $200 million, that is—it suits Turtle just fine. She's good at keeping secrets, and she won the game fair and square.
Ending #2 takes us to peek into the characters' lives five years later, when some of them have figured everything their lives out... and some are still working on it. Everyone seems to be "growing up," though, even the adults: businesses are successful, people are getting married, and characters are seeing rewards for their good deeds.
In Ending # 3, Turtle's with Sam Westing when he dies for real, and she finally becomes the heir. But it's not just Sam W who's bitten the bullet—several other key characters have passed away at this point. The ending skips so many years ahead from when most of the game takes place that the thirteen-year-old heroine's now a married businessperson.
It makes sense that the book would have to get to this point, though, since the original game was tied to the "death" of Sam Westing... and the winner can't collect her prize until the inheritance becomes available.