It takes imo 3 things to win AV with 40 toons:

1) Actually having 40 toons
2) Get them 40 toons in the same AV
3) Get the proper setup with enough healing and aoe dps. ( like ele shaman + resto shamans + resto druids + couple priest for dispells)

Getting 40 toons in the same AV works the same way as queuing up for a full premade WsG, i.e. both 5 groups queue up at exactly the same time, and only accept the queue if they all got it. If not requeue. Not sure how many attempts it's going to take to get all 40 in, but it doesn't look impossible. Definitely not when you queue up with more than 40 toons.

Then there are imo 2 options to have a win: either go kill opposing captain, and go back to your general and defend him to win by reinforcements. I don't really see how you gonna lose enough toons that way to not win by reinforcements. If they are organized they would just not enter the room and wait till 1 side gets bored. Which is not very likely.

The other option is going straight for the opposing general (eventually after whacking the captain first). But this takes tanks. The risk is that they have the towers down so they can engage your general faster than you can do theirs.

Should be quite fun to see that though. If there are muppets who need more evidence than the armory of both sides, you should simply ignore them.

gl