i think we have missed the point
In the chronology of the dark tower world when the gunslinger begins the world has already moved on and by the time Roland makes it to the tower the universe is at its exhausted end, on the very verge of breaking apart. And in my mind there can be no doubt that Roland does not just return the world to the slightly less dilapidated state that it is when he crosses the desert, he actually returns it to the beginning of time. as the reader are shown the beginning of the gunslinger only as a metaphorical return to the beginning a return to where we met our great gunslinger and began our journey. In Roland’s head his life started over from a baby, in shardik the bear’s mind it was his first memories after being made, for the universe back to the forging of the tower and the beams. Time is simultaneous in the dark tower hence the ability to switch between when’s never travelling forward or back but simply stepping through
The horn is the symbol of the beginning of the end to the endless cycle something even so tiny has changed and chaos theory dictates that that small change will ripple out and change other things it may only be one repetition it may be thousand but eventual when things are done correctly Roland will save the tower and restore the world with out returning it to the very beginning. The horn is a symbol of hope for poor Roland hope that one day he will be able to rest.
"Humanity does not ask us to be happy. It merely asks us to be brilliant on its behalf. Survival first, then happiness as we can manage it."
"We're going to just take it right out, and it won't hurt a bit."
Ender nodded. It was a lie, of course, that it wouldn't hurt a bit. But since adults always
said it when it was going to hurt, he could count on that statement as an accurate
prediction of the future. Sometimes lies were more dependable than the truth."