Thomas dying before they came to From might be the key to ending things. Julie story walked and made the call that distracted her parents leading to his death.
I know the theory that this is tied to Stephen King comes up a lot but hear me out.
Stephen King has several books that relate to From & I’m not going to get into all of them - just 4.
The Talisman, The Black House (sequel to The Talisman), The Eye of the Dragon, & The Dark Tower series.
I don’t want to spew all my thoughts so I challenge you to look into these 4. Just Wikipedia the plots and see what you think.
Stephen King becomes a key character within his own series in The Dark Tower. The last sentence of the series is the same sentence the series begins with. Insinuating the folks will keep going through the loop/reincarnating and forgetting what they’ve learned.
Even if Stephen King has nothing to do with From, I think there’s a huge clue in these stories.