Hurley helps Richard make his peace with Isabella, says they must stop the man in black

Back in the present, Richard makes his way back to the ruins where he digs up Isabella's gold cross. He looks up and starts yelling that he was wrong and that he changed his mind. He's opening that the man in black (Locke in this time) will hear him.

He turns around to find Hurley instead who tells him that Isabella sent him and she wants to know why he buried her cross. Hurley says that she is standing right next to Richard and that he'll tell Richard what she says. She wants him to close his eyes, just like she told him to do when she was dying.

She tells Richard that it is not his fault that she died and it was just her time. She says that he has suffered enough and when he says that he misses her, she says that they are already together. Isabella then disappears.

Hurley then tells Richard that she said one more thing. She said that they have to stop the man in black from leaving the island or "We all go to hell." We then see an extra-wide shot where we can see Locke looking over the valley where the are.

Again the question is, what havoc will be unleashed if Locke (the man in black) successfully leaves the island?