Originally Posted by
Hawkeye
I suspect you're correct, but I enjoy thinking about these things. XD
I'll take a crack since Yggdrasil decided to be rude about it. If you think about time like a string, if you create a branch in it that doesn't return to the main time, you fray the string and these branches end nowhere, but if you loop the string, you can create a knot that doesn't damage the overall thread and carries on after the knot. Having this knot in the string doesn't require that the two ends of the string also be connected. Basically only the events in the loop are predetermined in anyway and even then only with whatever factors are included in the loop, everything else is fairly malleable between itterations. Like how EMIYA participated in a grail war in his lifetime, but then manifests in a 5th war completely unlike the one he was in.
I hope that helped somewhat, I may have just rambled bullshit for a paragraph there, but tl;dr is basically that only the light novel and Kanata's presence here would seemingly be fixed factors, what happens to him after the set parameters of the loop could be entirely different from timeline to timeline from like Zelretch's perspective. We could debate the whole nature of freewill and determinism in this framework all the same, but for fixed points from an outside perspective you only need to consider the bare minimum to keep the loop intact, after that, anything else is open to interpretation.