The novel was a Thanatos Gambit by Al.
You see, at the end of IT, Ben did miss one of IT's eggs, and it hatched in 1985. This was Al. Wanting to avenge its mother, he went forward in time to 2011 and shapeshifted as Al. Al later used the time portal to try to go back to Derry in 1958 to defeat the Losers Club to no avail. He later needed someone else to take his place and made it appear that he had cancer so that Jake will go to Derry. The plan to save JFK was Plan B which he knew would result in a Time Crash. To ensure that this happened, Al committed suicide in order to inspire Jake to save Kennedy. After the Time Crash, Al would be successful and would defeat the Losers Club and IT continues its killing spree. JFK surviving could have made the Vietnam War better.
Unfortunately, using the time portal to change the past will always result in an equally bad or worse result as if time itself is some kind of Jerkass Genie. The events of the book foreshadow The Dark Tower
These strings are mentioned to weight heavily on time, to the point that they could destroy reality itself. Either Al's actions with the millions of strings he created, or someone else with another time portal caused reality to fall apart, leading into the events of The Dark Tower.