As others have said, on offense do not cap the south graveyard. I don't understand why something so counter-intuitive is in the game (you'd think capping it was a good thing but its horrible). There should be another workshop there to make it worth capping, or just removed to prevent confusion. To a new or inexperienced player this isn't evident until you're embarrassingly called out by your peers. Likewise if you see on defense that the enemy is capping the south gy, let them have it.
You aren't defeated until they touch the relic, so if they break the wall but are wiped you can still make a goal line stand to win (or if they went first, gain more time on your turn). I had a game where the enemy broke all the gates down but failed to click the relic after that. We decided to have fun and try to block them for as long as possible. Timely use of rogue stuns and saps, druid cyclones, fears, earthbind totems, hammers of justice, freezes, rings of frost, sheeps, deathgrips and even a well timed lifegrip of myself to an enemy so I could FN him extended our time by 2 minutes and we ended up winning on the next pull.
If neither team wins I believe the win is decided by who got the farthest so it's worth trying to at least break down one more wall if there's an iron wall defense on both sides.