Retrieve Contacts and Gmail Account - Broken Screen

Hi, my partners dad has a galaxy s3 where the screen remains black even though the phone is still receiving messages and calls, his work have now provided him with a new S5 and he wants to retrieve his contacts. The only thing is, he doesnt know what the gmail account is that he used, when setting up the phone he created one because he had to but has never used it since so we have no idea.

Is there any way at all of retrieving the contacts or finding out what gmail address is registered on the phone? Its a work phone so wont be rooted or have debugging and another obstacle is that he may have had a passcode lock on the phone.

Are there any software downloads out there or will KIES help at all? Im wondering if he may have a software update due and can run that through KIES which may hopefully fix the black screen somehow but thinking the passcode lock may stop us.

Really not sure what we can do, he has some contacts on there that he doesnt know and will not be able to get again.