The threat just feels empty to me. The T-800 just saved her life and is literally the only thing standing in the T-1000´s way of killing both her and John, not to mention Arnie is pretty much the main character. It feels like a cheap excuse to increase tension and suspense but fails miserably, that´s why I think its dumb.
Him interesting; you are correct that the film obviously was not going to let it happen so it felt sort of totally false suspense. But Sarah I think totally would have done it had not John intervened. We have to remember just how traumatized she must be by that thing. And obviously she doesn't trust it and feels they are better off on their own.
But I do get what you are saying that the effort seemed pointless and did not really provide a real pay off.