Look at the plot that resulted in the three-way tie in the underwater Defense battle. Clearly the universe of this fic allows absurdly complex plots to work when the plotters are of a high enough level.

Quirrel himself noted that plans that contingent on uncontrollable events tend to fail. Dumbledore wasn't counting on that plan working, as he said, "That's why it's important to have more than one plot going at once." The plan that resulted in the three way tie succeeded largely due to luck.