the Rav has resigned and will leave soon. In view of the fact that there is no other Rav in our congregation, who should take the lead in issues of halacha and day-to-day decisions?

Shalom, Thank you so much for writing to us. Firstly, before answering your question, let me advice that you should look for a new Rav as soon as possible. A synagogue certainly needs a Rabbi! As to who should answer halachic questions in the meantime- perhaps the best thing to do would be for the synagogue board to meet and decide on a temporary address for all synagogue questions. This could be another local Rabbi (is there a Bet Din in your location – perhaps they could provide a Rabbinic voice for you). Or perhaps an agreed upon Rabbi from another location. The main thing is that the Rav be someone who is agreed upon by the synagogue members, or by the board as the representatives of the congregation. When you decide upon such a Rabbi, you should contact him and ask if he’d being willing to fill in for a limited time. It should be stated and clear that he is being invited to give temporary rulings until a new Rabbi is found. And that his rulings are only binding until the new Rabbi takes over. This will make sure that there is no problem of having to “reverse” a ruling. The Rabbi should obviously be someone who understands your congregation, and is in line with it’s type of Judaism (you don’t want to go asking a Chabad Rabbi questions if your shule is Satmar, for example!). May you have every success. Blessings.