Except what happens to the audience if the arena is collapsing like that? And the arena still needs to be rebuilt for the next fight.
And if one mage surrenders, does that mean instant death, or just that he loses the match?
I think generally no matter what you do there's going to be a tiny amount of uncertainty about the outcome of an unfinished match until the last possibly point of damage is dealt, since attacks are through dice rolls. The only way to be certain is if they're taking upkeep damage that they have no way to prevent, remove, or stop receiving. Like say, Ghoul Rot and no dispels, purifies, or purge magic. But even then, unless that damage would kill them during their very next upkeep, you don't know absolutely for certain if they might be able to turn it around and kill the enemy mage before the Ghoul Rot takes them out.
Therefore, the best tiebreakers should be an extremely accurate approximation that predicts who would have won if the game continued. Some of the ideas already presented here look like they would do a pretty good job of that all things considered. Also, don't forget that since Mage Wars tournaments are in swiss format, the only ties that will need to be broken will be between the top participants, like first place, second place, etc., so that prizes can be awarded without tearing them in half. A win would be +1 to your tournament score, a loss would be -1, and a draw would be 0.
That being said, I think I can combine RingKichard's plan and aspects of Zuberi's and my own plans into a procedure for breaking ties when it is necessary to do so that is slightly more accurate. The idea is that the fairest tiebreaker is the one that most accurately predicts who would have won if the game hadn't gone to time, and that you can use the current game state at the end of the tiebreaker to predict where it would have gone with a high accuracy.
To review Ringkichard's original plan:
1. The final portion of every tournament game is reserved for tiebreaker play. In a 90 minute tournament game, the final 15 minutes is reserved for tiebreaker play. In a 60 minute game, the final 10 minutes is reserved. Prompt play during tiebreaker game rounds is strictly mandatory.
2. When the expiration of normal time is announced, the current game round is finished and the final three rounds of play begin. The game will end when the third game round finishes, or when final time is called.
3. The three rounds of Mage Wars Tiebreaker play proceed normally, with the exception that each player must record the damage done to his or her opponent. Each round, the player who does the most damage to the opponent's Mage (including loss of life, tainted, etc) wins the round and one of three possible tiebreaker points.
4. After three tiebreaker rounds, the player with the most tiebreaker points--two out of three--is the winner.
5. If, during tiebreaker rounds, one player takes damage in excess of his or her remaining life, that player loses as normal.
6. If a tiebreaker round is tied because neither player did any damage, or because the players did equal amounts of damage, no point is awarded.
7. If, at the end of tiebreaker rounds, the players are tied in round points awarded, the winner of the game is the player who did the most total damage summed over all three rounds
8. If both players did the same amount of damage totaled over all three rounds, the game is a draw.
9. If tiebreaker time expires without the completion of all three tiebreaker rounds, end the current tiebreaker round as it stands, and score it as above. The player who has done the most damage in the portion of the round that has been played scores the point. The player with the most tiebreaker points is the winner, as usual. If the points are tied, check total damage done during tiebreaker play. If that is tied, the game is a draw, as normal.
My addendum: If the game still ends in a tie after this process, follow this procedure for measuring and comparing average mage damage potential.
Here's how it goes...
1. Check your mage-damage potential (the total attack dice that could be rolled against you during the next rounds' action phases. So if a creature has a full action attack and you are in range of it, or if they have a quick action attack that will only take one move action to put in range, then the dice of that creature's attack count as part of your mage-damage potential. If you are within range of a conjuration's attack, that attack's dice is added to your mage-damage potential. If you are in a zone bordered by a wall with the passage attacks trait, your opponent must reveal any force wave, force push, or jet stream they have planned or spellbound. Check if you are in range of these spells and whether they can affect you. If they can, add the number of dice from the passage attacks to your mage-damage potential.
2. Find the difference between your life stat and your mage-damage potential.
3. Repeat the process for your opponent. Find the difference between their life stat and their mage-damage potential.
4. If the difference between your life and your mage-damage potential is greater than the difference between your opponent's life and your opponent's mage-damage potential, then you win. If your opponent's is greater than yours, then you lose. If it is still a draw, the player with initiative wins. If after that it is still a draw, the player with the most mana wins. After that, give it up; it's a draw whether you like it or not.
For this measurement we use average potential damage as the unit. So we'll assume the average potential damage to be 1 damage per die when the enemy mage has no armor, and then each point of armor reduces the average potential damage by .5 (to take into account critical bypassing armor and normal being blocked by it). If the enemy mage has incorporeal, the average potential damage is reduced by half.
