No way! It'd be a bit pathetic if she didn't complete the last 2 films, nobody else is Hermione. I'm absolutely shocked. At first I disliked her and her attitude, (not to mention her over-acting), then I grew to like her, now I think she's mental for not continuing!
Harry Potter MADE Emma Watson her, gave her her fame. Even if she does quit now, she'll still be known for that, so it's a bit pointless! And now on top of pointless, people will think she's silly and unreliable in the film industry as well.