[Luvian]

When they said judgement day is inevitable, to me, they said:

"Human are a greedy war-mongering species, no mather what they do, they will end up creating weapons they can not control". That's why no matter how often they destroy the uncontrolable weapon (skynet) it just delay the inevitable.

As for John Connor, he is not destined to die. In fact, he got killed because of what happened in T2. In the T2, when they told what would happen, John Connor did survive and lead the human to victory. But when they stoped skynet in the past, it changed the future in T3, and John Conor was killed because of his love of the T-1000. I'm pretty sure that after the event of T3, he'll be more prudent and won't be killed.