As to the question of what if B scored:
A live ball passed through A's basket (as JugglingReferee pointed out, teams shoot at their own baskets in Fed), so A get two points. At this point you're going to hit the whistle, get everyone straightened out on which direction they're supposed to be going, and give the ball back to B for a throw-in anywhere along the A's endline.
You're going to want to do this rather quickly, before B's coach starts whining about how you should've called over and back and not given them the basket.
Just a couple of little twists for your consideration:
- If B gets fouled while shooting at A's basket, the ball is dead immediately and B is not given any free throws even if the shot is unsuccessful (B would, however get free throws if B were in the bonus, but that was obviously not the case in the play you stated).
- If B shoots at A's basket from behind the three point line, it only counts two points.
Both of these little quirks are because shooting at your opponent's basket is not considered a try.