Can my husband cash out his 401k without my consent?

Usually you cannot "cash out" a 401k. It is an ERISA plan and falls under specific federal regulations that prohibit withdrawals absent some sort of special circumstance. You can take loans against it, however. It is possible for him to take a loan against his 401k without your consent. IRAs and Roth IRAs are different from 401k plans. They are not ERISA plans and, if you are willing to pay the penalties, you can cash them out any time with or without the consent of a spouse. If he leaves his job and converts the 401k to an IRA, then he can cash it out. If you have not attempted to settle your financial matters from the separation, or have not gotten a Court order resolving them, you should consider commencing that process immediately. Contact a lawyer as soon as possible.