[JRutledge]

In the back of the rulebook, the rules say the series is over if the defense gains possession of the ball. I would not say the ball is dead immediately, but if B gains possession I would think that would cause the ball to become dead. Without any specific information that I can find, I would say that the ball is not dead and if A gets the ball they can return the ball for points. Now this is of course if your state uses the NF procedure and does not modify those rules, which is what I have heard some states do.

Peace