If both houses switch then he will be distracted fighting them for the rest of his term; if they don't we no longer need to treat the US as a functioning democracy.
And then what? Things will magically go back to the way they were? I doubt it. The US has seriously damaged its international reputation. It has burned bridges. It has started literal wars. Removing the Orange Danger would be a good start, but it will by no means by the end the problem.
Exactly. Trump isn't the problem. Trump is a symptom. I'm far more terrified that the US will sigh and go "puh, glad that's over and will never again be a problem" than I am of Trump.