This is probably obvious, but while nonpayment of fees (or expenses) may under some circumstances permit a lawyer to withdraw from a case, it does not permit the lawyer to reveal confidential information. What does a lawyer do if (as sometimes happens) the client objects to withdrawal?
The ABA in ABA Formal Ethics Op. 476 (Dec. 19, 2016) (here), said that the lawyer should (a) in the initial motion say nothing more than “professional considerations” or the like; (b) if pressed by the court, point out that the court should rule without requiring disclosure; and (c) only if pressed or in the alternative, offer to provide the information for in camera review.