FYI, I succesfully restored all my WhatsApp messages using the WhatsApp Backup on Google Drive :D
How to delete your WhatsApp account without losing your WhatsApp messages
#1 Make a backup of your WhatsApp messages using the built-in function of WhatsApp in the WhatsApp app itself to your Apple or Google account.
#2 After you succesfully made a backup of your WhatsApp messages to your Apple or Google account, UNLINK / DISCONNECT your Apple or Google account from your WhatsApp account.
#3 After your Apple or Google account is not connected anymore to your WhatsApp account, you can delete your WhatsApp account if that is what you want.
To delete your WhatsApp account, use the built-in function of WhatsApp in the WhatsApp app itself.
DO NOT delete the WhatsApp folder on your smartphone.
Restoring your WhatsApp messages
#4 Make sure WhatsApp app is installed on your smartphone.
#5 Accept the License Agreement of WhatsApp and follow the steps provided by WhatsApp.
Because I left WhatsApp for a short time, I received some new WhatsApp messages from one of my contacts. This contact was sending a WhatsApp message to me while my account was deleted. I decided to delete these new messages.
I then went to the Settings and I make sure that my Google account with the WhatsApp backup is selected as the location for new backups and to search backups.
DO NOT make a new backup.
DO NOT press the button that says "Make Backup" (or something like that).
Again, I only went to the Settings to make sure that WhatsApp knows what the location is to make new backups and to search backups.
#6 Uninstall WhatsApp app.
#7 Install WhatsApp app again.
#8 You will be asked if you want to restore WhatsApp backup that is found on your Apple or Google account, don't skip this and choose to restore the backup.
#9 You have your WhatsApp messages back.
Again, usage of this tutorial above is still at your OWN RISK. Even though I succesfully have restored my WhatsApp backup, I did this within a short time. For example, maybe Apple or Google won't keep your WhatsApp backup unlimited, but for a limited time. I am not saying that this is the case, but I only say that you must always keep in mind that if you delete your WhatsApp account, there is Always a possibility that you won't be able to recover your WhatsApp messages.