A replacement or rework seems to be your only options, unless this was just an isolated spot (unlikely). If you decide to remove the carpet some day, and money for a new floor is unavailable, you can redo the existing floor by removing the boards and repositioning them to eliminate the gaps. You would have to install a few new boards to make up the shortage. Since they were never finished and in good shape, a light sanding before finishing may all that you need to do. Good luck if you decide to purchase the house.....