All true. However and fortunately, there are many mitigating factors that make it a poor target. First, there is good ferry transport between the Oakland and SF sides, and more capacity could be quickly brought online. The entire Blue & Gold and Red & White tourist boat lines could be temporarily pressed into service. Truck traffic could be forced south down the 880 and across the 237, and then only during non-commute hours. In fact, truck traffic should probably be routed that way anyway, given the circumstances. Much of the truck freight slack could be taken up by sending freight up the CalTrain tracks during non-commute hours. Might require some connector track, but manageable. Also, you can bet military based on Treasure and Yurba Buena Islands are watching both spans like a hawk.
The Bay Area is as resilient to adversity as any place in the country. What the scum will get by attacking bridges is a lot of capable, motivated, and p---ed off people.
The BART transbay tube would be closed to check for structural damage from a massive object of the bridge's size collapsing.
Most Ferry traffic has to go under the bridge to get to the East Bay (Jack London Square, Alameda). I don't think that ferrys can go under the east span. The only place the ferry could go would be Vallejo.
Not to mention the thousands of people who live on Treasure Island.
After the 89 quake, the Bay Bridge was out of commission for, what, a month? This is also an excellent telecommuting area. (And, G-d forbid they mess with the crush up in Napa!)