"Thanks to a quirk in the legal structure used to set up the SPDR S&P 500 ETF Trust, known as SPY, more than $250 billion rests on the longevity of 11 ordinary kids born between May 1990 and January 1993."
By law funds require a determines termination. They tied it to the death of "random" kids. The fund will end in 2118 or 20 years after the last of these eleven kids (chosen, "voluntarily" by their parents, as token people) dies
It' relatively clear and straightforward, but the article does not explain what happens when the fund terminates.