Yes, the law states that you can fill your tank in place with sand or foam. We will advise against this since it will be very diffucult to sell your property with a previously filled oil tank. Even if you have all the proper documentation from the company who did it plus the township approval.
The problem is, it is not required to sample around the tank before you fill it in place. A lot of the tanks that are filled where actually leaking before they where filled. So yes, you have all the proper paperwork but there still might be an unknown environmental issues in the ground.
NO. There are no laws on the books for residential heating oil tanks that state you have to remove it before you sell the house.
You will have a very hard time finding a buyer who will be ok with buying your house with the tank still in the ground. At minimum they will want to test the soil around it or most likely require you to remove it before they close.