On the topic of the consequences of using another director -
I admit I'm biased, (I've been a Jackson fan since Heavenly Creatures), but it seems to me PJ has an ability to get the audience to invest emotionally in scenes that, in another director's hands, would be either merely entertaining or unbearably "schlock-y". Yes, Jackson has been known to descend into schmaltz at times, but more often he pulls it off; he has a sort of childlike sincerity that draws viewers in; makes one set aside cynicism and feel for the characters. I think that ability was a major part of LOTR's success, and that The Hobbit is even more dependant on it.
PJ is the only director whose movies make me cry, and they do so repeatedly, from the murder scene in "Heavenly Creatures" to the scene when all of Gondor bows to the hobbits in ROTK, to the final scenes of King Kong. With any other director I would watch the first without emotion, and laugh at the cheesiness of the latter two. I'm doubtful that any other director will be able to give us a Bilbo we can love as much as we should, and that is absolutely essential.
As much as I dislike the prospect of a non-PJ hobbit, I'm even more distraught over the idea of a non-Serkis Gollum. Ian McKellen was an excellent Gandalf, and it would be a shame to lose him, but another Gandalf is concievable. Another Gollum is unthinkable to me - a sacrilege. If Serkis refuses, there are three possibilities I see:
1. An actor attempts to imitate the Gollum Serkis created. This sort of situation gives, at best, weak, empty results, and at worst, laughable ones.
2. Gollum is purely CGI, with only a voice actor. Hello, Jar Jar!
3. Another actor takes Gollum in a completely different direction; however, there aren't that many directions to go & still give us Tolkien's Gollum, so this approach would most likely give as a charater that is either too monstrous, or too shallow.
I hope what we're seeing with PJ and NewLine is, as Child says, part of a complicated dance, because if Pete and Andy sit this one out, we're going to end up with a version of "The Hobbit" that has two left feet.
*groan*