This needs to be investigated and if shown to be accurate, Roberts will be impeached.
No he will not, there is nothing criminal, if he indeed said it its just his opinion.
At most it would require him to recuse himself from future Trump litigation. I doubt this story, he's no fool even if he felt that way he would never come out and say it.
And?
By whom? Who do you think is going to impeach Roberts?
What are you smoking? No way the Democrat controlled House would even allow impeachment of an Allie on the court to come up. Roberts will not be impeached, even if he were the Senate would never convict him.