TC has a huge impact on the startup market. They are the most powerful tech news business in the world and can literally move the market on a startup with a single blog post. If it is positive your user numbers sky rocket and the VC's are calling. If it is negative your investors are on the phone asking questions.
The CrunchFund gives them skin in the game. TC will determine to a significant extent the value of the CrunchFund portfolio.
We read TC because we trust them to give an unbiased view of our startup world. Yes, MG loves Apple and he gets a lot of stick for it. But what if it came out that all of MG's pension money and savings were in Apple stock. It changes things, right?
If the journalistic trust between the publication and her readers is lost, TC's influence and readership will dissipate.
IMHO the greatest threat to TC is not Arrington leaving. It is the CrunchFund, and the erosion of TCs integrity and credibility that will come with it.