What Flowers said. Any accounts with a single named account holder (be they bank accounts, retirement accounts or whatever) will become part of your estate and be frozen until the estate is settled. If there is an executor for the estate, they may be granted power over these accounts by the court while the estate is being settled, but only to pay debts and bills pertaining to the estate, not to hand out lump sums to family members.
The only way someone's money reverts to the government is if they literally have no living relatives and no will or other document that might detail what they wanted done with the remainder of their estate upon death. Even then it can take a very long time before that money is released from the accounts.
The way to handle this isn't to go sticking someone else's names on your checks or opening joint accounts. Instead simply ask the bank for a Beneficiary Form, on which you can designate someone that would have access to the account in the event of your death. It's a good idea for married couples with joint accounts to have a third party beneficiary in addition, just in case you're both killed in the same accident or whatever.