The key word is that it doesn't LOOK like it drains...but under the assumption that it does...also, that would be really annoying if I finish fighting as Sora, but I need to switch to Riku. That is what the manual switch is for, but as some have said, I believe there will be a penalty for that since you are kind of breaking the whole concept of the drop gauge there.
I'd think that'd be it starting in the negatives possibly....I've found that one screenshot with Sora and the drop gauge being in the negatives a bit odd.
But if it's a penalty, that'd make some sense.
In thinking that someone who wants to play Riku as much as they can will switch back to him once it goes to Sora.
They'll do it manually, so then the next time they switch to Sora, they won't be able to manually do it, and they'll have to play as Sora longer.
I only see the drop gauge going in one direction...just a thought.