Yes, google will automatically pick a winner, as explained here in the faq (http://prizes.org/faq)
How does Voting work?
You may vote on as many contests as you wish. However, you can only vote for one entry in a given contest each day, and you may not vote for yourself. You do have the option to vote for more entries in the same contest tomorrow! If buyers don't pick a winner when the contest ends, winners will be chosen by popular vote.
How does Voting work? You may vote on as many contests as you wish. However, you can only vote for one entry in a given contest each day, and you may not vote for yourself. You do have the option to vote for more entries in the same contest tomorrow! If buyers don't pick a winner when the contest ends, winners will be chosen by popular vote.