They have no power now I doubt this will change

There won't be any grave crackdowns on conservative organizing, and things like Trump clubs (which allow right-leaning people to come together and freely criticize BLM and illegal immigration) will still exist. If Trump loses, even if Biden does nothing, it's likely that Trump clubs will dissolve, and there will no longer be anything like Trump rallies where right-leaning people can gather in mass numbers.

Why didn't that happen after 2016

It was, but it's currently being spun as a one-off or a mistake. Trump winning again will cement that it wasn't a mistake, and that conservatives genuinely want border enforcement and a stronger stance against far-leftism. Hence "vindication"

I don't think this even depends on what Trump does tbh - but on what he says and what he's perceived as. The image of a pro-border candidate winning is important for culture and morale. It says "advocating for strong borders is what winners do".

We already have riots rivalling the 60s race riots 2016 pales in comparison.

Fair

Trump and the GOP have enabled them already

My prediction is that if Biden wins, we will see policies an order of magnitude worse than we've seen under Trump. hence "catastrophic"

I'd say Trump is better but by no means good

This is basically my position. The real work has to be done by grassroots organizers on the ground, building a new culture. I've never said that Trump will save us, he's just meaningfully better than the alternative