There is redundancy in the form of a 90 minute Ro-Ro ferry route to the east, as well as mothballed docks near the bridge in case of an incident that closes the bridge completely. I’m not sure about the capacity for oversized loads on the ferry, but it’s often used by trucks to carry gravel and aggregate for construction.
more of a cost vs benefit tradeoff than a failure. It could also be just a SPOF for over-sized loads, whereas people have multiple routes on/off island.