Your US passport cannot be consfiscated because of a debt.
The fact that you live in another country does not mean that you cannot be sued in the US. Further, while it is more difficult, a judgment obtained in the US can be enforced in Europe.
I would recommend that you consider filing bankruptcy. While student loans are not normally dischargeable, they may be discharged if not discharging them would cause an undue hardship. This certainly seems to be the circumstance in your case. Obviously, an attorney would need to get more facts to come to a conclusion.
Please be advised that any information or advice given herein does not constitute an attorney client relationship. Further, before taking any actions or deciding not to take any actions, you should seek counsel of an attorney. This forum cannot provide you with the anyalysis and detail necessary for a full and accurate opinion to be rendered.
The US government is never going to revoke your passport because you owe a debt. As you know, when our country was founded, one of the big problems we had with England was the idea of debtor's prisons.
I think your financial adviser has given you rather radical advice about your student loan. I would recommend seeking a second opinion about ways to possibly resolve this debt, and am posting a link to the National Student loan website.
Hope this perspective helps!
Disclaimer: This answer does not constitute legal advice. I am admitted in the States of New York, New Jersey and Massachusetts only and make no attempt to opine on matters of law that are not relevant to those three States. This advice is based on general principles of law that may or may not relate to your specific situation. Facts and laws change and these possible changes will affect the advice provided here. Consult an attorney in your locale before you act on any of this advice. You should not rely on this advice alone and nothing in these communications creates an attorney client relationship.