If that were to happen they would divert traffic via the logging road network they've identified as being a substitute for such a closure but not suitable for a routine detour. Pushing vehicles through Sooke via Shawnigan would be a very lengthy detour and for many motorists it just wouldn't make sense, especially having to crawl along a windy logging road, at night, with on-street tires, etc.
They could very easily connect Goldstream Heights to Niagara Main and in to Langford via Shawnigan, but that also won't happen as the CRD is dead set against any such routes through the watershed, let alone the park.