If you lost the API Key, there is no way to restore it anymore. The webservice user, ws@Company.[YourCompanyAccount], is used to authenticate the payment request sent to Adyen. Therefore, if you lost the API Key and you are not using it anywhere to do payment requests, you can simply generate a new API Key.
If you are using the same webservice user for API requests somewhere and you generate a new API key then all requests will return the 401 HTTP response, so be careful to check if you are using your API Key somewhere before generating a new one.