On the homepage, there is an Export link at the top right: the content of the Wiki can be exported in HTML or more interestingly in Markdown. There are 645 files (2.9 Mio uncompressed).
I could backup the content once in a while, or even write a small script to do it automatically regularly based on such a command:
$ wget https://fortranwiki.org/fortran/export_markup
Remark: it saves only the current state of the Wiki content, not its history.
Maybe @Beliavsky could help contacting the maintainer (see Fortranwiki.org unavailable (now up again))?