Go down there, and buy for us from there so that we shall live and not die...
The possuk repeats itself here. Yaakov Avinu said that they shall live and not die. Living and not dying are the same thing.
The Ohr Hachaim explains that if they would not go and buy produce from Mitzrayim, they would not only die in this world due to their hunger, but they would also be punished in the next world. They would be sinning against their Creator by ignoring the hunger.
However, if they went to Mitzrayim, they would live in this world, and they would not die or be punished in the next.
Another explanation the Ohr Hachaim offers is that he was unsure if they would be successful in buying sufficient food for their needs. However, at the very least, they would be able to purchase sufficient food that they would not die.
He told his children to go down to Mitzrayim, where they may be able to buy enough food to live, or at the least, not to die.
