Google contacts party deleted, how to restore?
If you sync your google contacts it will add the contacts present in your google account to your phone, without deleting or modifying the other contacts (option b).

The reason might be that, you accidentally deleted all the contacts in your phone and restored the partially synced contacts from your google account.

How to restore? - I think you already restored the available contacts using your google account. You can't restore beyond those contacts, unless you had the other backup source (like you can backup your contacts using inbuilt option for contacts backup)