Netbox has many dependencies, ALL of which may be "affected" by an "in-place upgrade" (which is actually a "reinstall of the OS").
All the dependencies like SQL, webserver, etc., must be replaced by versions that are four years newer. Trying to keep older dependencies won't work on a Debian-based system -- some of those older version will be incompatible with the newer OS.
The changes to your OS and dependencies might indeed break something in your setup. We have not tested Netbox. There is no certain answer to your hypothetical question.
Advice: Create a testing environment that mirrors your current setup. Use cloning or backup to make your changes revertable. Then test the reinstall on that environment. It will take time: That's the price your organization will pay for waiting almost six years.
I wish the answer were simpler or easier. Sorry.