From
this support request; it was answered:
An account is considered active as long as it's owner logins to it from time to time (at least once in 6 month). Posting entries or comments is not a necessary condition if you at least log into the account. Please see the FAQ at [
http://www.livejournal.com/support/faq/127.html#inactive] for additional information.
*quote* However, LiveJournal may delete inactive and empty journals in order to free their usernames for the new accounts. In such cases, after these accounts are purged, their usernames become available for renaming. Inactive accounts which may be deleted are those containing two entries or less, which had not been accessed by their owner for 6 months or more. Journals and communities which are placed in memorial status, suspended or placed in "read-only" mode, as well as accounts with Permanent and Professional package of service, are not considered empty.
Duh.. I'm not a lawyer. The FAQ says my LJ isn't empty (neither is a paid account now called "professional package of service" as long it is paid). But is says "delete inactive and empty journals" so that's only 50 %. Or ???
Still waiting for an answer of my comment at the news post.