will signing out of icloud delete all my notes permanently?
You should be fine. Refer to: If you sign out of iCloud to get a better understanding of what will happen with your documents and data (including photos. etc).

However, if you're concerned and you have another device (such as an iPhone or iPad), you can ensure they are logged into your iCloud account so you can see/access the notes on those devices.

And of course, it goes without saying that you should ensure you have a backup regime in place (such as using Time Machine).