I updated the Terms and Conditions page today to clarify the situation with the long-term availability of blogs created on myblog.arts. See the section title ‘Blog and User Lifecycles’.
Unfortunately we have to prune old content in order to keep the system at a manageable size. However, there is the facility to export your blog if you are going to graduate, or will no longer have access to myblog.arts — and we give you plenty of time to access your content before we remove it. See the information here.