GM Ruling: Full banner score is counted for sudden death wins.
There are several reasons I have come to this view;
1. Precedent. - I recall a similar result for the Somosierra scenario but have no documentation for it. It must be prior to MT6. Moreover, and Michal K points out, this situation did arise in Ancients, and the ruling there was full banner count. At that time I put a post onto the CCA Yahoo Group, which I will reproduce in part here.
There are a few Victory Conditions that have come up here, or could come up. In some cases these relate to block elimination counting, which is only relevant to tournament tiebreaker counts.
Exit Banners (e.g Amphipolis)
www.ccancients.net/Maps/Peloponnesian-Wa...phipolis-422-bc.html
The Victory Banner is permanently gained by the appropriate side upon exit.
Exited blocks do not count as eliminated. Eliminated blocks from exited units do count as eliminated.
Named Leader loss (e.g Cunaxa)
www.ccancients.net/Maps/The-Spartan-Hege...4-cunaxa-401-bc.html
If the named Leader is lost, the winner scores full banner score (in this example, 7). Loser banners and all eliminated blocks are counted normally. Named Leader counts as 1 block.
Area Banners (e.g Sphacteria)
www.ccancients.net/Maps/Peloponnesian-Wa...hacteria-425-bc.html
The Victory Banner in this objective hex is gained when the appropriate side occupies the hex at the start of their turn. The Victory Banner is held and captured only as long as a unit of the appropriate side holds the hex. If the unit vacates the hex for any reason (movement, retreat or elimination) during its own turn or during the opponent’s turn, the banner is immediately lost and placed back in play in its original position on the objective hex.
Turncoat units (e.g. Tanagra, Mycale)
www.ccancients.net/Maps/Peloponnesian-Wa...-tanagra-457-bc.html
www.ccancients.net/Maps/Greco-Persian-Wa...7-mycale-479-bc.html
The Victory Banner for the unit counts as normal. Blocks eliminated are separated by which side owned the units when the blocks were eliminated.
groups.yahoo.com/neo/groups/ccavassal/co...ations/messages/2765
2. Where there is a sudden death victory condition, if the banner score is discounted for a sudden death win, it discourages the victor to achieve that goal, and opens up a manipulation by a loser to try and minimise the loss. (I'm not saying this has happened here, but I can see it could, and I know people that would opt for a loss minimisation if the option was available).
As to the desirability of sudden death victory conditions in tournaments, I admit they have problems. Generally I avoid them, but in the instance of a Semi-Final it seemed feasible, and to be honest I looked at them, considered 7 losses of 9 to get the sudden death and didn't rate it as a highly likely outcome.