There will surely be some, but the default case is likely "grandma stops watching Netflix". That's an "exodus" of people who weren't paying them anyway (and were consuming bandwidth). In a few cases, they'll pay more money for grandma. Netflix bets that this category is bigger than the one who quit.
Why would paying customers quit? To teach Netflix a lesson? I suppose it happens. Because they think AppleTV/HBO/Hulu is a better deal? I suppose that happens, too, but we're talking about products in the range of $10/month (or ad-supported) -- not exactly the kind of thing where people are going to find massive bargains.
There will be some exodus, to be sure. But I don't see any reason for a mass exodus.