Personally, I don't think that these bannings will lead to something as extreme as what you're describing. Specifically, I don't see this leading to a ban of reasonable people.
If I'm reading your thoughts correctly, your main concern seems to stem from the fact that you're assuming the goal is to stop these people from communicating with each other.
However, I don't think that's the point of these bannings. I think the goal is to stop them from reaching a new audience and expanding (however, as I am not a CEO of a major social media company, I can only guess what the motivations are).
In that sense, if everyone switches to using code words, or to using non-broadcast media (eg, Signal), it's significantly less concerning, and there will not be a strong push to ban people from those sites. By only de-platforming clear violators, I bet they can still have a big impact.