Well, I think existing ICO pages are remaining, but without ads, just for conversation and any updates for community
No way, Facebook is important media and community in ICO. The news of ico is spread out through Facebook community, groups, and pages. If Facebook is banned ico News can't spread the world.
Although Facebook is the number 1 social media now. But you were false when thinking that Facebook is an important media to promote ICOs. Most of good ICOs didn't run Facebook Ads to promote their project because it's usually not effective. Even they don't need to run ads of any media but they can still attractive a lot of people invest in their project if it's good.
Now, Facebook ads is the garbage ads that is including many scam sites, is trying to scam money of investors so i think Facebook ads ban ICOs is a good news for the crypto currency.