Since you haven't specified the country, generally it's a good idea to formally close the account.
If you have not done this for quite a few years; Assuming that no one operated it, most countries have regulations, the account would move into dormant status [generally a year or two years of inactivity]. Post this there is a period [generally 7 to 10 years] by when the funds into the account would be moved into Government Account as unclaimed funds.
If this is what has happened to your accounts, then there is nothing to worry.
The Risk part;
Given the account is inactive, before it went dormant, if someone fraudulently started using this account, then you are equally at risk. Given online frauds and illegal money laundering activities, your account may/could have been used by someone to deposit illegal money and transfer it somewhere else. There are instances where even Dormant accounts have been fraudulently activated in collusion with Bank staff and illegal activities carried out. In such cases although you may not loose much cash [as you don't have much in the account], there could be serious questioning by authorities about your intent. i.e. you have to establish that it was honest mistake and you were not part of the illegal activity and you were as such not aware of it.