Oh a judge could totally make a threat of some sort in private. “Listen. This is a big deal. This could be career-destroying. I’m giving you the option to voluntarily withdraw rather than having a public hearing to determine whether you will be sanctioned and/or removed. And I can tell you that my tentative is to have you removed and issue a very severe sanction.”I doubt it.
If the judge wanted them removed from the case, then I think she would have done it publicly. Threatening an attorney with something privately in order to get them to 'voluntarily' withdraw would be pretty unethical.
Moreover, it would be really strange to call a public hearing, approve cameras in the courtroom, make it open to the news media, have the victims' and defendant's family come, etc if her intention was just to force the defense counsel to withdraw beforehand.
And she couldn’t know that the defense would acquiesce if she did indeed suggest they voluntarily withdraw. So she had to prepare for the hearing to go forward.