Hi. I have JIRA 6.4, soon to upgrade to 7.6, in test .... I think this works to identify JIRA accounts:
select * from cwd_user where
ID not in (select user_id from cwd_user_attributes where attribute_name = 'login.lastLoginMillis')
and created_date < SYSDATE - 90
and active = 1;
...but am - scratch that - was unsure how to make those accounts inactive.
This was for an Oracle back-end, but I assume it'd work in other platforms.