Yeah, I guess that eventually they would probably starve to death...But dreams have no real concept of time so they might be able to live full lives inside their dream before they physically die. Sure, it'd result in the death of the human race (except for the people who didn't see the moon) but that would also mean world peace lol
And Warren, the whole Zetsu thing had nothing to do with the Moon's Eye jutsu. That was the Nativity of the World's Tree afterwards that wrapped them all up. If Obito just left them all there and that thing never happened, then technically they wouldn't become Zetsu (though they might drown if they were looking up and it started to rain lol).
So who knows how long the dream would last, but it was supposed to always be a peaceful and happy dream. As long as it wasn't a forever dream with nightmares, then it wouldn't end up like pic related ---
(Junji Ito's 'Long Dream'. If you haven't read it, it's pretty good spooky stuff considering we're in the month of spooks and scares. All of his stuff is pretty fun though lol)