Facebook will remain an "ads" company for as long as it's profitable. Marketing dollars will always need go somewhere, so I'm not convinced the advertising market will just wither and die in the face of adblockers. As long as Facebook commands an army of eyeballs, its advertising business will be profitable.
Facebook has shown a willingness to diversify its social properties via synergetic integration. See: whatsapp, instagram.
Facebook will likely continue to diversify its business. For example, it could easily repurpose its excess hardware to enter the cloud computing market and compete with AWS/GoogleCloud. I would be surprised if this is not on the roadmap.
Yes. As we've seen, the only way to stop such things, is for the next disruptive company to come along and fuck their shit up.
Something will likely come along. My guess is that it will be spam-related, which will make the FB user-experience too difficult to use to get a quality experience. FB will try to appeal to government for protectionist legislation, but it won't happen fast enough.
The question is if you can hold out long enough and if the change you predict will happen fast enough.
That can get expensive quickly, so it's not quite the inverse of holding stock where the only downside is how far the stock can drop, not how far it can go up.
Google may have a chance of beating Apple at #1 but Facebook has quite a margin.
Essentially both Facebook and Google are ads businesses. Facebook seems to be optimizing for short term growth at the expense of their brand.
I know many people who joined Facebook around 2008 and absolutely were big fans of it. After 10 years none of them even use it, the novelty wore off.