You made a starter, that means the yeast IS viable. That's the major point of making a starter, to let you know the yeast is alive and well. Unless between making the starter and pitching it you either froze or boiled your yeast, there never is a reason to believe that modern yeast, especially with a starter would suddenly cease to work.
It just isn't like that, yeast are amazing and resilient creatures that can survive and singlemindedly do their jobs. In fact the current strain of yeast called "Cry Havoc" of Charlie Papazian sat for nearly 20 years in a fridge. He had a jar of infected yeast, that he put away to study later, and forgot about it, and it got piled in the back of his keezer or beer fridge, forgotten. 2 decades later he stumbled upon it, and for ****s and giggles made a starter with it, not expecting much. To his surprise it worked, and when he brewed a batch of beer with it, he even found that not only did it work, but 1) the wild yeast that caused the infection long died out 2) and it made for an extremely crisp and clean beer.
People have also cultured yeast that was trapped in amber for thousands of year. And recently grown yeast and fermented beer in space.
So that's why I always find it so amazing, that even despite making starters that prove the yeast is working, many new brewers can't seem to trust these amazing creatures.
The biggest problem, and I think by it now taking off as you posted (which I didn't see when I started writing this,) is that WE HUMANS think we're in charge, and we try to impose OUR timeframes on them. We expect the yeast to work when we want it to, and expect it to finish at the exact moment the instructions say it will. But as I say all the time, yeast can't read, they don't know what day it is, they don't know the time. They don't know we have a deadline (which we shouldn't) so if it doesn't act exactly how we think it will, even though we know the yeast is fine. We immediately think something's wrong.
When usually the only thing wrong is our lack of faith in them.
You got a lesson today of something we usually forget, yeast are wild creatures, there is always some wildcard factor at play.
