If I sell my Chometz with my local Rabbi and then travel for the whole Chag of Pesach, do I need to leave my house key with the rav in case the non-jew who purchased it wants to collect it. If so, and I did not leave him the key, does the Chametz revert back to me as soon as the non-jew was unable to gain access?
The sale of chametz is based off a tosefta where it is clearly a real sale. It became common in Europe for Jews in the whiskey business to sell their chametz before pesach and buy it back after pesach. It was clearly a full sale though, since often the gentile would drink some of it on pesach. Therefore, to show the sale is real, you should make sure the gentile has access to the chametz. However, if you did not leave the key, its possible that the sale would still be real, but it would likely depend on many factors. It would be a good idea to ask a rabbi.
Per the Young Israel Rav the keys should either be left with him, or with someone else in town while we are away, as long as he knows who has them, in case the non jew wants to get the chumatz.