Do you mean, what happens if you balefire yourself? Ask Lews Therin. Actually I don't think it would be possible to balefire yourself, since you would then have stopped channeling before you balefired, unless you somehow managed to boomerang the balefire so it didn't hit you for several seconds. LT either used a different weave or died because his grassy plain had become a volcano.

If you balefire your companion in a circle then they would die. The link being broken before you started to weave, but the weave still having existed, I'd say that if you were drawing as much of the power as possible that you'd then end up having drawn that power yourself, and burning yourself out.

But it is very possible I am talking complete nonsense and I hope someone comes along with some properly thought-through theories. It's an interesting question.