I would keep the oil and add heat pumps. It will cost you nothing to leave the current heating system in place. More affordable heat pump systems can be a bit lacking when it is extremely cold. We have heat pumps at work. During really cold times, we have to set the heat on the high side before the cold sets in for it to keep up. They are a pretty affordable option, but unless you get a really good system, I'd want oil to supplement here and there.