Hello, I left a house that I am renting more than a month ago and left some chometz behind. I am planning on selling the house for Pesach (I will not return to the city that the house is in until after Pesach). Should I make an effort to get someone to throw out the stale cookies I left behind?
You can rely on the sale of chametz to a non-Jew, though it remains preferable to throw it out, if this won’t involve a major effort.
It is possible that even if you generally refrain from selling absolute chametz, in this case you can rely on the sale, together with bittul of the chametz.
An important factor in this question is the fact that you left home more than thirty days before Pesach.
The answer to the question will apparently depend on a dispute among rishonim concerning somebody who left his home more than thirty days before Pesach, whereby the obligation of bedikas chametz does not apply.
According to many rishonim, under these circumstances it is sufficient to rely on bittul, and there is no need for bedikah and bi’ur. This will apparently apply even if the person who left the house later remembers that he left chametz at home: he can rely on bittul, and does not need to perform bi’ur.
According to Rashi, this might not be the case, but the interpretation of Rashi’s opinion is disputed by later authorities.
Please see here for details of this dispute.
Yet, it is possible that this dispute only addresses somebody who left home without knowledge of the chametz. If somebody leaves home with the intention of leaving the chametz over Pesach, it is possible that all agree that bittul is not sufficient.
Moreover, the Mishnah Berurah (448:25) writes that a person on a ship, who remembers that he has chametz at home, should sell it to a non-Jew. He makes no distinction concerning when the person left home, and the implication is that one should not rely on bittul alone, and should ensure that the chametz is sold to a non-Jew.
Therefore, one should ensure that the chametz is sold, but there is no obligation to go to lengths to actively get rid of the chametz.