The domain name is up for purchase ($9999.99 according to my registrar), so it looks like it’s lost rather than just temporarily parked for a slightly overdue bill.
Luckily the site was recently backed up by the Internet Archive and the archived All, gpx, and csv links seem to work.
The GPX file seems to be truncated at 1MB, but the CSV file seems to have more entries.
I imported the CSV file into a Google My Maps, then exported KMZ from there into GaiaGPS for my own use.