You don't say if this is a Christian couple or not, but as a Christian I will say that Biblically every reasonable attempt should be made to keep the marriage together. There is certainly a Biblical "exception clause" for the case of infidelity, but even then divorce is permitted, not required. And while there has been some speculation on the part of respondents, I don't see a clear statement by the original poster that infidelity actually occurred.

Here I most agree with CountrySquire's advice, "If I were the wife I'd tell hubby to attend marriage counseling with me. If he refuses, then let him know to expect the papers." Whether the immediate ultimatum is for counseling or something else on the path towards resolution, I would say that, Christian or not, she will feel better and more comfortable with herself in the long run if she has made every reasonable effort to save the marriage before going through with ending it.

On the other hand if this is indeed a case of "unrepentent infidelity" and it's clear hubby has no intention of changing, then she should certainly not be encouraged to go on in false hope.