Determined by butterfly

As our current technology improves explosively, sooner in our future, we may possibly succeed in going back to the past. While if so, at this day, theism (at least Christianity) will collapse. Let me elaborate.

As Christians we have some core beliefs - one of which is the uniqueness of individual creation. We believe that God has created us with intention, given us freewill to make choices, and imposed on us his plan of our lives.

Then, if there is a single person succeeded in travelling back time and changed something, it proved two concepts simutaneously:
1) Determinism is correct.
2) You can reverse - and take the role of - God's creation.

According to the butterfly effect, even a tiny change in the past would lead to a drastic change in future. The further you travel to past, the more different the current world would be. So, if one has travelled back 100 years, he killed someone randomly - the entire family at current time will break down and vanish in no where (if unlucky enough, he may have vanished as well). While at the same time, new individuals will appear due to the change in marriages. So, you utterly cancelled God's creation, and replaced with your own ones.

How about the proof for determinism? Think deeper, the butterfly effect per se has this implication - our life is determined by our past experiences.

In response, I have two choices. Either I believe we human can never travel back to past (which might hold true at least for 100 years I guess), or I believe, even if we can travel back, we cannot change anything.

For either, I need a big leap of faith, gosh.