Facebook's forward growth is going to come from persistently leveraging the userbase with a continued, gradual slowdown in growth. They don't need to diversify their revenue stream, they're growing sales at 30% and are larger than Oracle. Their social monopoly is going to make it very difficult for them to do meaningful acquisitions freely (unless they're well outside social). They couldn't easily buy the next YouTube, WhatsApp or Instagram at this point due to anti-trust concerns.

They did selectively start buying back shares recently as a form of capital return. I'd expect that to continue to the extent the stock remains modestly priced versus the business growth rate.

If all they do is keep on the same path, they easily get from here to $100+ billion in sales by doing nothing special beyond what they're already doing. Plus ~$35 billion in profit to go with it.

A mere 6% average sales growth per year for the next ten years gets them to $100b in sales. More likely, they get there in fiscal 2022 without much trouble.