It's never ban people
Are you sure? I could have sword I heard that facebook banned ICO and crypto ads a while ago.
When Social media bans ICO & Crypto ads, what will be the best way for companies to advertise and inform?
The best way will probably be on crypto specific sites like this one to target people already familiar with the concept. Also crypto news websites. In that sense not much changes. But to target new people they might have to move back to more traditional media where historically all the advertisement was focused before social media grew into what it became.