It's not clear to me how Facebook stops their current public affairs debacle. The situation Mark and Sheryl find themselves in currently provides no natural policy opposition to execute a FUND (fear, uncertainty, and doubt) communications effort. Ideally, when managing such a campaign you have a black hat and a white hat - you have good guys and bad guys.
Right now Facebook is the black hat and the bad guy.
If I were running political communications and public affairs for Facebook, I would work on three fronts.
One, I would do all I could to secure center-right and libertarian think-tanks and thought-leaders with messaging and advocacy to not allow the government to "halt innovation and the promise of the internet."
Two, I would drop millions, and millions of dollars on STEM education and training programs targeting endless identify political groups, especially center-left organizations that work with women, minority, and under-served economic communities.
Three, I would harvest thousands and thousands of stories how Facebook makes someone's life, more profound, more prosperous, and better. I would amplify these personal stories endlessly in paid and owned media to generate earned media. Facebook needs a coast-to-coast echo chamber with a clear message that the platform is a useful and necessary tool for modern life.
Honestly, all this might not be enough to save Facebook.
Facebook has little reason to exist beyond distracting its users, allowing advertisers to secure unlimited commercial sales data, and providing a platform for Russian operatives to disrupt democracy.
Facebook needs a path to wearing a white hat and being one of the good guys, fast.