The point is, does the paladin has an opportunity to fall as a result, or is he forced to fall as a result, whatever he does?
The second opportunity is rather unpleasant from the roleplaying perspective. If a paladin tries to do good as far as the game allows him, but falls anyway, I consider this an unfortunate design decision.
The first opportunity is more interesting, but then the quest has to be re-written entirely, to include the possibility of the knights collaborating with you, to introduce another motive to confront Firkraag, to determine Garren's new role in this quest in all cases, etc, etc. A lot of work, and I am not sure it will be worth it in the end.