There is an 'ending ' of sorts in the boo, SK talks about a young couple that buys the house later in-spite of the ghost stories, and they have a dog. I don't know if this means Louis did die, or if he and Rachel ended up in the woods. It is clear someone finds out something though. This is why I wished Pet Sematary had some closure. Even if it had been a collection of other stories about the town and the people who used the place.
If I had to guess, the best case scenario of closure for Louis would be somehow avoiding (or beating) charges along the lines of murder, manslaughter and arson. Only to move away from town to try and start anew but spend the rest of his days enduring whispers, stares, anonymous notes and phone harassment no matter where he lives.
I don't recall Gage being reburied after the failed experiment in the woods. Where is the body? That poses a problem.
The Baterman fire was determined to be set years before, it won't take (presumably) more sophisticated law enforcement during the present Creed-era that long to determine the fire was set at Jud's.
Authorities either find reanimated Rachel walking around, the body of a Rachel killed for the second time or no body at all with Louis feebly explaining she went to get groceries and never came home or that she had left him. This leaves Rachel as a missing persons cases with the police. None of those scenarios bode well.
One closure scenario I wouldn't rule out is that Irwin kills Louis in blind rage over Rachel's death/disappearance, presumably before any arrest or sentencing. His character was capable of it.
Like others have said, there are a few remarks where Louis seems to look back on these horrors in the past tense. If I had to vote, any defense lawyer, court judge and jury worth their salt see that Louis is now a nutjob and label him "insane" which probably keeps him out of prison.
My firm conclusion is Louis Creed ends up in a place just like Juniper Hills just like Henry Bowers did.