If it were me, I would have privately (emphasis on private) worked my way up the chain of command, trying to alert more and more people that there was a serious problem brewing.
The meeting in the story was obviously going to be a failure. So if you’re in a situation where you know that X is going to fail, doing something other than X is advisable. I would’ve tried to work with the deputized team to come up with a smaller plan that could be executed in, say, three months, and then figured out how to sell it to management in a way that three months isn’t a dealbreaker.
Alternatively, I would have gone to management ahead of the meeting and let them know privately what they should expect to hear. That way they’re not completely surprised when you’re in Zoom, presenting a 12 month extension, and they have to say something. “It would be career limiting” is about the best thing they could say.
You want to give them a better alternative. And giving management good alternatives is arguably the job of line engineers like us. We’re a part of a team; our job isn’t merely to do what we’re told, nor is it to say blatantly that a project is doomed. There’s usually a middle ground.