My understanding is that there should always be a chief available. Like the other posters said, the chief can be a child, even a 2 year old! The chief can be a nursing mother, if this is the case you have to wait til she is done nursing and has put the baby down, then let her try again...and the new child too. With that many villagers, going thru the detail screen one-by-one is an option or, what I do, is pause the game and move all the villagers to the robe. If some walk away, put them back in case they didn't get to try. If this doesn't work quit the game, re-open and try again.

I know some of this is a repeat of info but it really should work.

Good Luck!