In the early days I made a project with battery backed RAM as NVM - both code and data - and a very good supervisor, and serious Vcc decoupling of all chips, nothing else. This ran till the batteries wore out (10 years) without a glitch.

Today I probably would not risk this, but the fact that this ran (and is still running with fresh NVMs) does say something for the supervisor/decoupling scheme.

Have fun,

Erik