For your reference, you may want to read this article first: http://askfrfrancis.org/qa/burial-at-sea/
As mentioned in the article, the Church does prefer body burial over cremation. However, understanding the pastoral situation of each place, the Church today does allow it given the proper care is given to the cremated remains, namely, that it is placed in a permanent place of rest.
As for the burial place being reused, I wonder if the bones may be gathered before the rent is cut? They do that in Hong Kong so the bones may be cremated. Otherwise, we just have to accept that eventually, our body does have to go back to dust. We treat the body with dignity the best we can, and allow nature to take it back.