In case you decide to try it again, I wrote a little Selenium script in Python that works pretty well (although it took 3 days to complete for about 12 years of FB posts) https://github.com/weskerfoot/DeleteFB/blob/master/deletefb....
It's true the posts could be archived by Facebook or another entity. They could conceivably be republished widely by a bug or someone malicious. But at least this way they won't resurface in the normal course of business.