Bitcoin anonymity ends when you need to convert this virtual currency to old good bucks. However, there are still some options available to resolve this issue. First, you can keep the virtual currency and use it on darknet markets. Second, there are special tools called anonimizers which can mix multiple addresses and transactions in order to launder Bitcoins.
Currently, there are about 32 bitcoints on those accounts which equals to ~ $55,000.
Here are the WannaCry Bitcoin accounts: