I doubt Arnold will lose especially with polling showing it that close. The only way to unseat Arnold is for the Dems to run on specifics that the people want otherwise Arnold will be back again.
The rule of thumb says that the incumbent should poll over 50%.
I hope in the coming months Arnold's numbers will go up.
The US Chamber of Commerce started some good ads for Arnold. At least they are not waiting until it's too late, which it the main reason the Special Election Propositions went down in flames, the unions ran nasty ads unopposed.