I don't know if it is legally confirm. But I'd suggest you to keep following in mind. When you delete a decryption key, it is impossible to guarantee that there is no copy of this key. A copy could be done purposely, e.g. as a back up. A copy can be also stolen. You cannot prove that a copy of the key does not exist. Thus despite deleting the key there is Risk that data can be decrypted. I would discourage you from using it.

What are alternatives? There are multiple standard procedures. One of them is based on multiple rewriting data storage with random data.

I don't know if it is legally conform. But I'd suggest you to keep following in mind. When you delete a decryption key, it is impossible to guarantee that there is no copy of this key. A copy could be done purposely, e.g. as a back up. A copy can be also stolen. You cannot prove that a copy of the key does not exist. Thus despite deleting the key there is a risk that data can be decrypted. I would discourage you from using it.

What are alternatives? There are multiple standard procedures. One of them is based on multiple rewriting data storage with random data.