I would personally go with a 10 second retroactive 'idle' countdown after time is up in the case of a tie or heavy combat where the tide could turn. If the battle looks close as the timer runs out, the fight continues until there is 10 seconds of idle time (no major damage being dealt to a ship that could possibly kill it in the next ten seconds).
This would basically be a 'players in motion' or 'ball in the air' type of rule set.
Rules would be:
1. In the case of a tie, combat will continue if both teams are active players in heavy combat and have an equal number of ships in the air. If either team breaks off and combat stops for 10 seconds, the match is decided by a random toss.
2. In the case of a tie while combat is idle and both team have an equal number of ships in the air, the match is decided by a random toss.
3. In the case of a tie while combat is idle as time runs out and one team has an more ships in the air, that team is declared the winner.
3. If teams are separated by 1 point, combat will continue ONLY if the team with fewer points has both ships in heavy combat (dealing large amounts of ship-killing damage) and is in a position to score two points. If they only score one point and tie before idle combat, the other team wins without a random toss.
Subset rules.
Heavy combat shall be defined as something that could kill a ship in its current state in 10 seconds or less. Otherwise, it is strategic combat.
Disabling guns or engines does not count as heavy combat.
Popping balloons does not count as heavy combat unless the target ship is on the ground with armor down.
Random toss could be flipping a coin or sending the official a 'rock-paper-scissors' call in a PM.
The time extension ONLY APPLIES to ships currently engaged in heavy combat when the 20 minute timer runs out.
Ships that respawn after 20 minutes is up may NOT rejoin combat.
If a ship is in respawn countdown when the 20 minute timer run out, it may NOT rejoin combat.
If is ship is not in active combat when the 20 minute timer runs out (even if it's ally is), it may NOT engage in combat.
If a ship leaves combat (takes or deals no damage for 10 seconds) it must leave the combat area and may not engage in combat.
Breaking these rules decides the tie and forfeits the match.
That would feel more fair to me, though I generally only sub for these matches.