Posted by: bunyip
Among the theories of what it is that 'time' is is the concept that it is all laid out and we pass along it. This eliminates the notion of freewill as everything that is/has/can happens has already happened. In this scenario the past is fixed as much as the future and if at some point it was arranged that the past became non operative in some fashion, ie, time travel was no longer possible, then the future and the past would still remain the same.
If you used some other theory of time, say, in which time is essentially the front of the wave of possibilities becoming actalities, ie, the past, then this does not rule out an action whereby all future time travel was impossible.
But it would leave past actions untouched. Unfortunately this leads to such convoluted worldlines that I don't think I will ever be able to unravel it, although if you take each individual's worldline from their conception to their death you end up with world lines passing through 'the present'. As the present is not set these world lines would become just another factor in determining the probability of any event. If so, then the fact that time travel had occurred in the past would not be prevented.
I'm off for chocolate now. that was too much intellectual effort.