Theists: How can predetermined fate and free will coexist?

[RozKek]

If god has already seen it happen, prior to it happening, how can you do anything different when that time comes? 

The play has been written prior to your arrival, you can only act the part given to you.

I think you're thinking of it in terms of Him traveling back and forth in time and whatever He sees when He "travels" to the future is how things are set in stone to be regardless of what might change. Such is not the case. He knows what happens because He exists in a dimension outside of time, meaning He is already seeing the entire span of time and all the actions we choose to take all at once.

And if he sees that all your actions will lead to you going to heaven in 20 years, can you still end up in hell?

Edit: -CL replied, answering in another post-