1) If your husband was overpaid--that is, he received money to which he is not entitled--then he has to repay it. If he and the employer can't work out a payment plan which they both can agree to, the employer may sue him for the money.2) Any overpayment of taxes is something you should be able to get back by filing an amended return--speak to an accountant or tax preparer about this.3) Generally speaking, the employer may get back any money overpaid to your husband, including money which went to taxes (see #2, above, for how to deal with that). Anything which then needs to be backed out of benefits (e.g. if overcontributions to a 401k need to be returned), you husband should then in turn be able to get back from the benefits administrator, insurer, etc. upon proof of the overpayment. It  may take time to resolve, but ultimately, you should be left in the same place as if there was no overpayment.