You think he won't be able to reach people because Twitter won't give him an account?
What the internet has enabled is cheap publication by anyone to anyone. There's no reason to have a corporation as gatekeeper to what gets onto the internet, and that won't happen. It's very easy to create alternatives.
I don't think Trump will be back as a political force, but that's not based on the ability of Mark Zuckerberg to keep him hidden from us. I think it's that enough of the American people have woken up to where his style of demagoguery leads.
In other words, I'm counting on the intelligence of the American people to keep him out. That's kind of a risky strategy.