Not all spouses commingle their funds. Some maintain separate savings and checking accounts. There's no law against it, but if your wife dies and leaves behind a savings account in her sole name, who gets the money might become an issue. It depends a great deal on the laws in your state and any provisions she might have made to transfer the account at her death.
Court intervention is required for any assets a decedent owns in her sole name. They have no way of passing to her beneficiaries or her heirs without the probate process, which changes title and ownership. Your wife may have bequeathed her savings account to one individual in her will, or she might have directed that her beneficiaries share the value of her entire estate. As part of the probate process, the account would go to whomever she designated to receive it. If she bequeathed her estate in percentages, such as half to you and half to her child, you can request that the account be transferred to you as part of your share of the estate.
Even if your wife didn't leave a will, probate is still necessary to transfer ownership of her assets to her heirs. Because a court has no way of knowing who your wife wanted her property to go to without a will, states have laws -- called "intestate succession" laws -- to determine who receives her property. Typically, a decedent's spouse inherits first. If she has children or if her parents are still living, however, you probably won't inherit the entire estate. You'll most likely have to share it with them. Intestate succession may not guarantee that you receive a specific savings account as part of your share. It only means that as a spouse, you'll receive a percentage of the estate.
One problem with probate is that it can be expensive. The court not only transfers ownership of the decedent's assets; it ensures that all your wife's taxes, debts and probate expenses are paid as well. Payment for these things comes from her estate assets. Liquid assets, such as savings accounts, are usually the first source for funds. Courts typically liquidate tangible personal property and real property as a last resort. If your wife left a cash savings account, the money might be used to pay creditors, taxes and expenses so other assets don't have to be sold. Some states have statutes in place to prevent this, however. In these jurisdictions, the surviving spouse is entitled to a dollar amount of personal property off the top of the estate before anything else is paid, and this would include at least a portion of the savings account, depending on its balance. The surviving spouse may also entitled to a living allowance for a period of time after the decedent's death, which could be granted in the form of the savings account.
Some assets can avoid probate, even if they're in the decedent's sole name. If your wife gave you rights of survivorship when she set up her savings account, the account will pass directly to you without court involvement or the necessity for probate. This practice is also sometimes known as a transfer-on-death provision. If the account holder dies, the account automatically reverts to the individual she named to receive it.