Hey everyone! I just talked with Rob Hinkle on the PvP team about this, and he let me know that:
1) Yes, right now, if neither team breaches the first set of doors, the winner is determined randomly (in case anyone wasn't sure).
2) We have a change coming that will determine the winner in this case by taking each team's number of kills into account.
Thanks for posting to let us know your thoughts on this topic!
Thanks for an official response on this. This issue has raised eyebrows since beta, and is long overdue for a fix.