After 120+ years I would NOT consider a cartridge [25-35 win] "dead" or "dying" or "failed".
Although old with low sales now, it has had a long career. Think I'd call it a success...
Being a dead cartridge is not the same thing as a failed cartridge. Marilyn Monroe was wildly successful, but she's definitely dead.
I wouldn't call the 25-35 Winchester "failed" because as you point out it had a long run as a popular cartridge. However, nobody has chambered a regular production rifle in it since what? WWII? so it's definitely obsolescent.
Winchester has 25-35 ammo on limited production, which is not a good sign. Hornady, God bless 'em, has just introduced a new load for it, so it's not obsolete. At least not yet.