There's a simulation theory that describes reality as being a synthesis of P2P interactions, and I've developed a similar theory of my own along those lines.

First, all possible quantum timelines exist, but a person's consciousness chooses a path through that infinite landscape. This rectifies physical determinism with free will. Reality is actually both.

Second, when individuals meet, their previously independent quantum realities "merge" such that the unknown known facts of one person's world are collapsed to agree with the known facts of the other person's world. For example, maybe you've never heard of or visited a small town, but if you meet someone from that town, their chosen reality of that town becomes yours.

Third, if a group is experiencing a timeline together, it's sort of a group choice as to what quantum path they will go down. This is why group prayer and meditation have been shown to affect reality.

What a time traveler like Titor would be doing by "changing the past" is pushing people's consciousnesses onto a better path...and assuming his own consciousness is somehow rooted with those consciousnesses, if he returned to the future, then he would be entering a better timeline himself.

There would be no cause-effect paradox because with this model all possibilities exist, therefore Titor would simply enter a reality where he successfully made the journey.