Correctable error situation?

[Scrapper1]

This supposedly actually happened, although I didn't see it myself. Just want to see what people think about it.

4th quarter, 3.5 seconds remaining. Team A is leading 54-52. A1 is fouled, but not in the act of shooting. Team A is in the bonus. A1 attempts the free throw, which is unsuccessful. B5 rebounds the miss, outlets to B1 near midcourt. B1 releases a try (obviously a 3-point try). The horn sounds clearly after the ball is in flight, and the try is successful.

Team B appears to win 55-54.

Before the officials leave the court, the table informs the officials that Team B had 10 team fouls and A1 should've been awarded 2 free throws.

The officials decide that the error is correctable. They disallow the 3-point basket, put 3.5 seconds back on the clock, and award A1 the second free throw. They allow the teams to play the make or miss. A1's second free throw is unsuccessful, B5 rebounds the miss and passes to B1, but B1's heave is unsuccessful this time.

Team A wins, 54-52.

1) Was the error still correctable, since the horn had sounded to end the game?

2) If so, should the officials have negated B1's 3-point field goal?

3) If so, should the officials have put the time back on the clock?

4) If you answer "no" to any of these, what should have happened?