Hi Tim,
Author of WP2Static here.
Whilst it may work for an archive of a BBpress site. I would suggest looking at HTTrack, an open source tool, specifically for converting sites to static.
There are versions available for most every known OS and you can even install it on your webserver to allow it to scrape the whole site quicker.
https://www.httrack.com
If you try WP2Static and it works for this use case, please let me know!
If you need help with using HTTrack, also happy to help.
Cheers,
Leon
