Looking at things from a pragmatic POV, would it be realistic for the Williamstown Dockyard to be re-opened and effective? IIRC one of the reasons why BAE ended up closing the facility was that it was no longer really large enough to handle vessels larger than ~120 or 130 m LOA, and there was no economically viable way to expand the facility. If the workforce has dispersed by either moving onto other workplaces and/or retired, and the physical facility itself is both too small and would need to be updated/refurbished before being used again, then I do not see a way for Williamstown to be made useful again absent a prolonged conflict requiring a whole-of-nation response.
It is both a cost and time issue. There would be costs associated with acquiring the site and then making the infrastructure fit for purpose again, or significantly greater costs (and time) involved if the site were to be expanded so larger vessels could be worked on. IIRC the Adelaide-class FFG's were close to the max size Williamstown could build. Good for their time, but frigates and destroyers now are more into the 140m+ LOA, and 6,000+ tonnes displacement range.
I suspect that establishing the sort of skilled workforce such a hypothetical naval yard would require would take longer to raise and train than reconstruction would, unless the yard were to also be significantly expanded. Pretty much the only way to get skilled workers for such a facility would require either conscription of workers from mining industries, and/or poaching already experienced yard workers from other Australian yards. As little as I like the apparent plan to establish a naval construction facility in WA for warship production, I think that will be more efficient and effective than trying to get Williamstown back into service.
If there were to be any serious efforts made to get former Australian yards back into service, Codock in Sydney would be a better idea IMO, as the site, whilst space limited (it is on an island after all) did already have facilities large enough to construct ~150m long AOR's with full load displacement of 18,000 tonnes. These facilities would need to be refurbished or rebuilt in some fashion, and of course the workforce established but I suspect the end result would be a more useful facility, provided gov't could and would continue to sustain the facility by placing orders for work. Given Australia's boom-bust cycles for naval construction and the apparent demise of the national shipbuilding plan, I am dubious about Australia managing to keep Osborne and/or whatever ends up built in WA going as a viable, functioning facility.