Based on what i saw, read, done and observed, many PPC's who are giving pain in the ass to their publishers will be put out of business. There're too many options that if you're PPC company, you should give flexibility with your publishers and not be ass like you are the only one doing this kind of business. I won't even touch them if thats the case.
Google won't have to worry about publishers leaving the network until AdSense has viable competitors. Right now, a bigger concern is keeping advertisers from opting out of content ads. That's why any "flexibility" needs to be on the advertiser side: e.g., by giving advertisers greater control over where their ads appear instead of requiring them to take whatever Google chooses to define as the "content network."
Even if Google can keep click fraud under control (and I think it can, for the most part), there's still the issue of lead quality. And, of course, some advertisers care where their ads run for other reasons.