If it passes, they will disappear in general elections, and for all practical purposes. The Libertarians, the Pacific Greens, the Constitutionalists, and so on, will vanish, along with pieces like this one from OPB.
Supporters might understand this, and figure it’s a price worth paying. That’s ok; you can plausibly argue that they don’t matter if they aren’t going to win. I bet a lot of “yes” voters are going to be surprised.