Quit two jobs as the solo dev at small companies because the cofounders changed their “product vision” before we finished most features. Nothing more demotivating than building something that never gets shipped.
I get a stable salary just for doing my stuff with (mostly) independence. If they want to never use it then that's on them and it's their loss. I still learned good lessons by working on it and that knowledge I'll have until my grave.
To me it's a win all-around. I can and will mention it during meetings if the right moment rolls around but won't insist or push hard on using the about-to-be-abandoned code. As a good colleague I'll point out an inefficiency that slows down product launch. If that gets ignored then I shrug it off -- the leader was given the info and chose their present course despite of it. It's their prerogative.