God never changed His mind about destroying all life through the Flood. He just told Noah to build a big boat so he and his family could be saved and mankind would be reborn through him and his family. Abraham nearly talked God out of destroying Sodom and Gomorrah, if if he had gone further in his negotiation with God, the cities would have been saved, but God saw Lot's righteousness and got him to safety. Moses talked God out of destroying Israel and starting the nation all over again through him by reminding Him of what the Egyptians would say about God going back on His promises to Israel.
All people who are presently lost are under condemnation. They are condemned already, but the prayers of His saints can change His mind about the people they are praying for. We can intercede for them, and Jesus takes our prayers and adds them to His intercession, and God changes His mind and decides to do the work of the Holy Spirit to show them how to get saved through Christ. This is the importance of intercession for the lost, because if we don't intercede for lost souls, they may stay lost when they could be saved as the result of our prayers.
So, if God can change his mind as the result of a saint crying out to Him to save a city or a nation, then we can cry out to God to save lost people and know that He will save them as the result of our prayers.
The problem is that most religious people don't spend the time to intercede for the lost, and that is why more people are going to hell when they could and should be saved.
One day, those who are lost will cry out to Christians in the judgement and say, "Why did you not pray for me when God could have shown me the gospel as the result of your prayers? Why did you not love me enough to see me find a way to avoid hell?" How would we be able to answer those questions?