The fact that God knows the future doesn't mean that we don't still choose it. If he reveals something to us, does that mean our choices will make no difference? I think there are a lot of ways the future can play out, and all the prophecies still be fulfilled. We can choose the worst possible route, or we can choose the best possible route.
We know the Savior will not come in a year in which the rainbow is seen, as Joseph Smith explained at least twice. Prophets have given counsel about a years supply since Brigham Young, and we can obey or disobey it. The prophesy will come true, but what it will mean in the lives of the Saints will depend on our choices.
The pioneers knew the dessert would blossom as a rose. But there were a wide range of possible fulfillments for that prophesy. The pioneers innovated and used irrigation to bring water to plants in dessert ground. God knew what they would choose, but it was they who made the choice. Maybe they could have hauled water instead. The prophesy would still have been fulfilled - but the result would have looked a lot different - it would have been far harder on everyone and the dessert wouldn't have blossomed as well. But it could still have blossomed enough.
We face many coming prophesies found in the scriptures. The vast bulk of us, even many of the best of us seem to feel like it is a play script that is laid out and there is nothing they can do about it. But we can choose how we will fulfill those prophesies.
If we choose apathy, our descendants must suffer for it. God will not simply go "uh oh, better make some adjustments" and fix things to match a divine play script . Our posterity necessarily suffers the blessings or the curses brought by their progenitors actions.
If we choose valiantly and protect our freedoms, our descendants must be blessed for it. Again, God will not react with an "oh shoot, they are messing everything up" and make some changes so the divine plan can proceed as prophesied. Our posterity will be blessed by our actions if we will choose to act valiantly.
There is room in the prophesies for an enormous range of possibilities. The ones that will happen will be the ones that we as a people choose. Our actions are not merely those of puppets with no ability to change the plot or story line. We ARE the plot. We ARE the story line. We are the main character because only we have the Holy Ghost and the priesthood. Because of that, no one can be the hero in our place. We CHOOSE the story our children will enjoy or endure. The only question is what sort of ending will we leave for our children to pick up from?