That's not fate, it's balance. Cause and effect, just that you are seeing the effect before the cause. One thing that exists because of another. The time machine was created by the machines. And thus the terminators are in the past. What makes judgement day happen isn't clear, but whatever happens happens, because judement day happened, the machines rose, time machines were invented by the machines, and here are the terminators. So, as long as the terminator is there in the past, judgement day happens. The former does not exist without the later. Same with time compression. Edea absorbed Ultimecia's power, and that couldn't not have been possible without Time Compression and Ultimecia's defeat. And so, time compression will happen because Edea absorbing Ultimecia has already happened. The later does not exist without the former, and since the later has already happened the former must happen or the later does not exist. And since the later does exist, so does the former.