It's not clear how long the project lasted but it was at least 3.5 years. So the time-line couldn't have been that rigid; yes there was a Gantt chart but those are like horoscopes. And since the requirements kept coming in there was no fixed scope.
As far as the customer goes you can say something like "we'd like to deliver a prototype early" and then it sounds like you're exceeding the contract. You just have to get them to prioritize features while avoiding discussing the fact that it's impossible to deliver all the features they requested. Basically you treat the lists as a wishlist rather than a requirements list. Maybe you come clean later once they like the prototype.
I'm not saying it would have saved the project, I'm just saying it's better than giving up and saying "the project is doomed" like OP did. But maybe OP wasn't cut out for a leadership role.
As far as the customer goes you can say something like "we'd like to deliver a prototype early" and then it sounds like you're exceeding the contract. You just have to get them to prioritize features while avoiding discussing the fact that it's impossible to deliver all the features they requested. Basically you treat the lists as a wishlist rather than a requirements list. Maybe you come clean later once they like the prototype.
I'm not saying it would have saved the project, I'm just saying it's better than giving up and saying "the project is doomed" like OP did. But maybe OP wasn't cut out for a leadership role.