If I understand you correctly (you didn't provide any examlpe data), this query provides the data you want:
SELECT a.*, u1.Name, u2.Name FROM `articles` a
JOIN `users` u1 ON (a.id=1 AND u1.`id` = a.`authorid` )
LEFT JOIN `users` u2 ON (a.`updaterid` IS NOT NULL AND u2.`id` = a.`updaterid`)
u2.Name
will be NULL
if a.updaterid
IS NULL` (or the updater-user is deleted) or will hold the name otherwise.