I've disabled all auto WordPress updates on my website because I like it that way, knowing that I won't make any setting changes later. So my question is, will it stay functional like that forever?
If you are on shared hosting (ie. some one else is maintaining your server) no it will not necessarily stay functional forever. Wordpress is designed to support certain php version (https://wordpress.org/about/requirements/). If you fail to update WordPress and your hosting provider updates PHP to a version higher then your site may stop functioning, same with the back-end database.
If you are in total control of your server, then hypothetically yes it will work forever. However there are downsides with this, the biggest being security updates. Hackers routinely scan for sites with outdated Wordpress versions to exploit known weaknesses. This is particularly bad for Wordpress because of the sheer number of people that use it means there are lots of easy victims.Not only that but each plug-in, or other software on the server may have security holes that can get exploited.
With all that in mind it is highly recommended to perform automatic updates, but turning them off shouldn't break anything, it just leaves you open to hostile attackers. If you haven't already, install a plugin like All In One WP Security (https://wordpress.org/plugins/all-in-one-wp-security-and-firewall/) which can notify you of people trying to guess your admin password, my tiny blog with almost no visitors routinely received a dozen or more attempts to hijack each week until I started doing extra security like renaming the admin page and blacklisting repeated attempts to log in.
No Its your Option you want to update to new source code or not. you can use Update Manager plugin to manage your updates with in wordpress admin area.
Thank you