Apart from that being very hard to script satisfactorily, it's also rather Romano-centric. Why Hannibal? Why not any other general? Hannibal's march is remembered because it was something very extraordinary, dependent on the decisions and daring of one man. Scripting it in assumes that it would have happened even when Hannibal himself would not have been born.

In any case, Hannibal and his army did not appear out of nowhere. They had been campaigning in Iberia for a decade or more, and directly provoked the war which Hannibal's march was intended to win. I don't see that happening with a script. He'd just materialize in Italy (cause I imagine the A.I. won't be inclined to march him to Italy if he appears in Iberia).