I said it before, and I'll say it again: People are not (all) stupid. They can adapt to changing circumstances. This is one of the bedrock assumptions underlying the surface/transit option: Tear down a freeway, and people won't just sit in traffic---they'll find alternatives to driving alone.
But the argument works both ways, and surface/transit opponents should acknowledge that. Instead, they're crying wolf about gridlock on downtown surface streets if the state charges tolls on the deep-bore tunnel. Just as people will find alternatives if you tear down a freeway, they'll find alternatives if you charge tolls that are prohibitively high. Those alternatives are hardly limited to sitting in gridlocked traffic. They include things like: Combining trips (stopping by the grocery store on the way home from work instead of making two separate trips, for example); driving at different times to avoid traffic on surface streets or peak-period tolls; working from home; walking or cycling instead of getting in the car; and taking transit.
This is, obviously, an argument against the deep-bore tunnel: If people can adapt, we shouldn't spend $4.2 billion building a highway so that they don't have to adapt. But it's also an argument against the reflexive notion that if you toll the tunnel, tens of thousands of cars will descend on downtown and cause devastating gridlock.
(Tunnel opponents point out, correctly, that "just take the bus" isn't an ideal option under the current tunnel plan, for two reasons: 1) Buses get stuck in the same traffic as cars; and 2) Metro is cutting service, not adding it, and the tunnel plan doesn't include ongoing money for transit operations. While those are legitimate objections, it's still true that many people have alternatives besides taking transit or driving alone.)
Which brings us to the Carmageddon-that-wasn't. Because people are adaptable, they found alternatives to driving alone on surface streets when the freeway closed down. Instead of hopping in their cars, they stayed home, walked or biked instead of driving, took transit, and found other alternatives to driving alone. Anecdotally, Streetsblog LA reports that it was one of the most pleasant weekends to get around on LA surface streets that they could remember.
Granted, that was only a two-day, weekend, experiment. But it speaks to the fact that people—in a city of 10 million people— can adapt, and do. We've adapted to highways that take us everywhere at lightning speed, we can adapt to tolls, and we can adapt to no highway at all. The flaw in the tunnel opponents' argument is that they argue people are smart on one hand, while assuming they're stupid on the other.