I recently lost my phone and all the WhatsApp chats, photos, and videos are gone. Luckily, before I lost my phone, I enabled the backup daily via Google Drive.
I bought a new phone and installed a new WhatsApp on the phone, and after verifying my phone number, it says that it had found backup at Google Drive and asks if I want to restore it, I push yes. The backup is around 400MB and it finished restoring the backup. I looked at the WhatsApp chat, it only shows group chat and all its content are empty.
I checked the file storage, and it has msgstore.db.crypt8 file in /sdcard/WhatsApp/Databases/.
I finally able to restore the chats, complete with photos, and videos after I clear cache at the settings > app > WhatsApp. Then, click on WhatsApp app again, it will asks you to reverify your phone number, then it will restore, this time should take quite fast, less than one minute because the backup files are already in your phone.
One thing to note is, the backup will go back to the state where it is last backed up, so the chats, photos, and videos you received from your last back up (the last backup before the phone is lost) till you do this restoration will not be in the backup.