The only thing I can tell you now is that one of the eggs Bill was destroying (it's been a while since I have read this part, hope I got it right) survived; Bill simply missed it. It eventually hatches and gives birth to a young It. After growing up a bit (which is fast, since time is different for the thing) it makes its debut in Derry on Halloween, falls in with a group of trick-or-treaters. It's dressed as a clown (or maybe something else, who knows). Eventually, it takes out all the trick-or-treaters it is with and goes to one final, isolated home and knocks on the door. A family is inside. It feeds.
That would be the prologue. The rest? I just don't know. I will say that there would be interlude parts, but instead of being the history of Derry, it is the history of It...as well as dispatches from the future of It. I'd also say the sequel should not be as long, or soap operatic (although having the children of the Losers fight the second It might be symmetrically satisfying).
Not bad, but
it's Ben who squished all the eggs while Bill squished It's heart. Richie gets kinda sqooshed under the dying It and then rag dolled.
I'm thinking more a movie sequel. Since the Turtle is Pennywise's natural enemy, Flo & Eddie could be the heroes of the saga. Has there been a SK comedy made yet? Give it the Bill and Ted treatment. Pick characters (and the actors who played them) from other SK works to help in an epic adventure to defeat It. And make it a musical while we're at it.
Gotta agree with Rick! It's so terrible it's good!