Here's the bottom line on the significant but under-publicized retirement of Melanie M. Darling, the California Public Utilities Commission judge who fined a huge utility $16 million late last year for not reporting secret contacts with PUC officials including herself: The PUC is rid of a major embarrassment, but is still under criminal investigation. Why? Because private phone calls and emails between some of its top officials and executives of Pacific Gas & Electric Co.