The actual idea we form, and consequently reason concerning, when we talk about "going back in time" doesn't appear to be any different than if we were to imagine letting time continue to operate normally while we used some unimaginably amazing machine to physically rearrange the entire universe to sufficiently resemble a previous state.
In situations like this I like to remind myself that our idea of time is derived from the succesion of our perceptions. An idea of time by itself can never be conceived alone by the mind, but always attends some perceptible changes in our ideas or impressions.
Form an idea of a white obelisk, for instance. Consider this idea in and of itself, unchanging, and it will never give the impression of time. Now imagine some changeable object with which to compare it to, the clouds moving behind it, and the idea of time presents itself. But as the idea of time is not distinguishable and seperable by the mind, to be considered on its own, I conclude that it would be more proper to call time a sensation. Time is a sensation we receive when we perceive change.
Why am I rambling on about our idea (sensation?) of time? Because if we are to have any consistency in our reasoning concerning time-travel, we must be able to form clear and concise ideas about what time-travel is or might be, and that starts with an understanding of our (idea?) sensation of time.
Proceeding in this method then I run into difficulties LONG before I find myself pondering a time-travel causation paradox. Indeed, I'm not even sure it is necessary to assume the existence of an external counterpart to our internal sensation of time.