[CaptainCrunch]

Its a machine and and AI not a creative or philosophical thinker. In the original time line the biggest threat was John Conner, eliminate the threat and that threat will more then likely be replaced by a weaker threat.

In terms of the calculation goes, Skynet was inevitable, even though the date changed and the method changed (from hardware (T1, T2) to virus (t3, SCC)) man was well on its path to computerized warfare using AI. Cyberdyne was already in motion in T1.

Even with the death of John Conner or Sarah Conner, the original time line doesn't change, the original machines that still send the Terminator back were still defeated, however in a alternative timeline judgement day doesn't happen until much later.

The machines were pragmatic, they knew that their existence was inevitable, Conner wasn't part of the calculation of its existence, just of its defeat.

I remember in one comic book that John Conner became female and Jane Conner when the machines sent back another terminator to stop the pregnancy by killing Reese before he got to Sara.

Sara still get pregnant and married and never knew about Judgement day but her daughter because the head of the resistance.