The question seems to assume the Genesis account is literal, so I'll answer from the YEC view, which assumes it's literal.
The usual disclaimer - not all denominations assume the Genesis account is actual history, I'm just answering as if it is, since the question seems to be looking for that viewpoint.
From Genesis 9 (KJV)
8 ¶ And God spake unto Noah, and to his sons with him, saying, 9 And I, behold, I establish my covenant with you, and with your seed after you; 10 and with every living creature that is with you, of the fowl, of the cattle, and of every beast of the earth with you; from all that go out of the ark, to every beast of the earth. 11 And I will establish my covenant with you; neither shall all flesh be cut off any more by the waters of a flood; neither shall there any more be a flood to destroy the earth. 12 And God said, This is the token of the covenant which I make between me and you, and every living creature that is with you, for perpetual generations: 13 I do set my bow in the cloud, and it shall be for a token of a covenant between me and the earth. 14 And it shall come to pass, when I bring a cloud over the earth, that the bow shall be seen in the cloud:
In the above passage, God promised to never send another flood. Therefore, if God cannot lie, there is no chance of Him flooding the earth, so it would be futile to ponder whether He would tell us ahead of time.
However.. God HAS promised that He will judge the earth in the future.
From Revelation 21 (KJV)
1And I saw a new heaven and a new earth: for the first heaven and the first earth were passed away; and there was no more sea. 2And I John saw the holy city, new Jerusalem, coming down from God out of heaven, prepared as a bride adorned for her husband. 3And I heard a great voice out of heaven saying, Behold, the tabernacle of God is with men, and he will dwell with them, and they shall be his people, and God himself shall be with them, and be their God. 4And God shall wipe away all tears from their eyes; and there shall be no more death, neither sorrow, nor crying, neither shall there be any more pain: for the former things are passed away.
2 Peter 3:10 even says how it will happen. It will be with great heat, not water. (Again, KJV)
But the day of the Lord will come as a thief in the night; in the which the heavens shall pass away with a great noise, and the elements shall melt with fervent heat, the earth also and the works that are therein shall be burned up.
So, we can say that if God were to destroy the earth, He would warn us - because He already has.