You will want to make backups of the sites you own or host for others. Don't confuse the journal with a backup strategy. The journal tells others how the pages you decide to keep got the way they are. If you loose pages, the journals go with them.
If you backup files on your laptop then the files in .wiki should get backed up too. Check to be sure. I use Apple's TimeMachine to backup hundreds of wiki sites on an hourly basis.
If you have a site hosted in a farm you can back that up by exporting the whole site as a json file. You can use curl or just SaveAs from the browser.
curl http://dork.wiki.org/system/export.json >backup
If you host sites for friends you want to keep then you should make backups for them too. The rsync command will do this efficiently over ssh.
rsync -avz root@dork.wiki.org:.wiki/ backups
An export.json file can be constructed from pages backed up with rsync using the jq utility.
(cd backups/site.dork.wiki.org ls pages | while read slug; do jq '{key:"'$slug'",value:.}' pages/$slug done) | jq -s 'from_entries' > export.json
If you write pages that people like then they might just last forever without any additional work on your part. Good pages will take care of themselves in a Darwinian sense but these 'selfish pages' aren't doing this for you.