You'd have to look in the backup file and see if there's anything backed up after 01.10.2018 in the file. Since WhatsApp doesn't request root, whether the phone is rooted or not makes no difference to WhatsApp.
Unless you used another app to do the backup, and it did request root access. Then you have to find that backup and check it.
But WhatsApp, by itself, doesn't care if the phone is rooted or not. It either backs up to its own folder (in which case you need root access to get to the backup - only root and WhatsApp have access to that folder, or it backs up to a folder readable by the user "everyone", so you don't need root access to get to it.
But it all depends on what you used to back it up. (Shell doesn't back anything up, unless you ran a shell script to do the backup. If you did, read the script to see where the backup went.) Oh, and never depend on the only copy of anything being on the phone - as you've seen, if the motherboard goes bad, you lose everything. Always back up to at least a cloud account (you have a Drive account if you have an Android phone) and a PC, laptop, thumb drive, something. Backing up to 2 or 3 cloud accounts doesn't hurt either. (Google had an outage almost a week ago. If you had needed your backup then, and it was only on Drive, you might have had to wait a day. If it's also on another account [I use Mega - it's also free], you just get it from the other account. I wouldn't use the Samsung cloud for anything important, because if your next phone isn't a Samsung, you have no access to that account.)