My belief is that causality loops are forbidden by the nature of the universe in that time only moves in one direction, forward. I reject multiverse explanations because they are inherently untestable — it’s no better than invoking gods. However, I also believe that if some way of traveling into the future is invented, the instant it works, temporal chaos will increase eternally because more and more and more and more people will vault into the future — forever. Plunging further and further ahead trying to escape a time so crammed with hordes and hordes from the past.
Now, because time does move forward, I do not believe such a cataclysm is impossible.
Finally, I nonetheless find the explanation that Hodor becomes Wylis as he dies quite convincing and satisfying.