Will the probe be intentionally crashed anywhere? Or is keeping space decontaminated not an issue here since temperature and radiation will sterilize anything in that kind of orbit?
Surface contamination is not an issue for Mercury or Venus. It is only considered a Category I (Mercury) or II (Venus) risk, which essentially means don't worry about it too much. Also, its orbit will take it very close to the Sun repeatedly. Eventually it will lose control due to lower fuel and the entire spacecraft will be heated to a more then high enough value to sterilize anything.
Most likely they will simply continue to do as many close passes as it can. If they can get a closer approach then they will try it. If they can't, it will basically melt except for the heat shield and a few other components, and might end up in Venus or the Sun.