I agree, except that Uwe Boll could
in fact frak it up...
...but I do trust PJ to figure out what works and what doesn't -- when push comes to shove he'll do what's best for the film even it means admitting he made a mistake.
Unless he's so far committed to it that he can't back out.
Besides dumping Stuart Townsend after filming began, Jackson scrapped several weeks of work on the Battle of Helm's Deep when he decided that Arwen shouldn't be there, and then there were extensive reshoots in early 2002. If the past is any guide, Jackson has no problem throwing work out and starting over.
The one place that Jackson really needed a reshoot that he didn't do was in the battle at the Towers of the Teeth where he superimposed a cave troll over Sauron. The problem is that Viggo was bathed in light on set (since Sauron was glowy) and he was acting in reaction to what was scripted to be there -- Sauron -- not what ultimately ended up being there -- a cave troll. However, I think by mid-2003, when Jackson realized that ending with an Aragorn/Sauron battle, was not the way to go, it would have been too difficult to do a reshoot.