a story needs dramatic tension to even be a story. Predestination is not a story. Creating a story where the PCs cannot lose is as much a railroad as taking the decisions out of their hand. No chance of failure and/or death means there is no consequences for the choices they make, and therefore not much of a story. There is no point in them making choices if the choices are meaningless.
Losing characters is not fun. So is going through something that has a predetermined outcome. If I already know what is going to happen, that my character will win no matter what I do, then how is it fun. I beat it, yay, so what, it was never in question.