To the best of my knowledge, noone ever left the project during its lifetime or raise major concerns about its worthiness. The team members themselves were dedicated and supportive of the effort. It is possible that some of them lost faith at some point but, as you say, but I was not aware of it. I was 2–3 layers of management higher and didn’t talk to the team members on a regular basis. I will ask the managers below me to comment on your question as well as I’m sure they had much better visibility.
Of course there were grumblings once in a while (not frequently) from team members working on other projects or from other teams across the company that we worked with. But this has happened with every single project I’ve ever worked on — I can’t think of a single project that was universally praised by everyone. Sadly, none of these grumblings ever resulted in the management team (including myself) reconsidering their decisions. We had deliverables, we had dependencies, we had deadlines. Damn the torpedos! Full speed ahead!