Mr. Popo's immortal, but his duties are only to take care of the lookout and not protect earth so he'd wouldn't help anyway.
and him testing SSJ Trunks or whatever in the Buu saga was filler
--
http://img708.imageshack.us/img708/3824/5959429725f9ecccb086.jpg
http://www.yourgamercards.net/trophy/a/CaptainRockman.png