Miriam recently had her blog locked out for awhile, see her post about that here.
I have no advertising on my site so I am not overly concerned about this happening to me but my blog could still disappear or be blocked for reasons beyond my control. I sometimes write my posts in a word processing document that gets saved (all of the letter transcriptions are done that way) but many of my posts were simply written in the post editor, so no other copy was made.
Once a month (more or less) I have been copying all of my posts to a word processing file. This method does not save all of the comments unless I copy them also and comments that get left after I have made my copy usually don't get added. I also subscribe via email to both my posts and comments and therefore have a back-up in an email folder. However I did not start this until earlier this year so anything written before that is not there. The best thing about the email option is that it is automatic which is great for someone like me that suffers from CRS (Can't Remember Stuff.)
Miriam backed up her blog by using WordPress. I followed suit and now have another copy of my blog online. I have set it to private for now. Even though many of the templates offered are very nice, I don't think I'll be switching to WP in the near future as it is very limited in how you can layout your blog and what you can add. Most of the widgets I use here are not allowed there. I am happy to have another option and will probably stop copying to a word processing file.