Does God still plan to use the nation of Israel to bring salvation to the Gentiles even after Israel failed?
Yes. Although Israel dropped and blew its opportunity, that does not cancel God's stated intention. The record shows He still intends to use the nation of Israel to yet bring salvation to the Gentiles, even though Israel's unbelief left her in an opposite role from what God originally intended.
Les explains that this was Israel's prospect, but history shows Israel dropped it and blew it. Nevertheless, that failure does not take away the fact that God is still intending to use the nation of Israel to yet bring salvation to the Gentiles. In the Old Testament verses under discussion, there is still no hint of the Church Age; God is dealing with Israel. God had wanted to funnel Israel back into the pagan, polluted stream of humanity and thereby purify it, but because of Israel's unbelief, the arrow goes down into the stream of Gentile humanity in a complete opposite role from what God intended. Les also notes that Christ's three years of earthly ministry were spent only with the nation of Israel, never outside the land.