I have thought of this every since Halo came out. It's not possible, of course, unless you use honor rules which is clearly too much to ask for from most Halo players. You would be able to put last man traits for each side and everything. It would be so epic.
I've thought of that, Though never came up with the werewolf and vampires. Too bad there isn't an option for that on Infection.
I know how this could be done! Sort of. Give everyone one life. Revive player on team by killing enemy. While it wouldn't be exactly the same, it would still have the whole, one side must be decimated thing.