Just musing along with you here but I think it's really hard for anything like that to happen. What seems at least halfway likely is that Valve won't be the same post-Gabe. But there will be other companies that end up with a similar ethos, and we can support those companies as best we can.
I'm a huge fan of the OSS model of keeping your core business fully unrelated to OSS but allowing and encouraging the use and contribution to OSS by people on your payroll because it really is a rising tide effect. There are just too many stories of a cool project becoming a company only to eventually reverse-robinhood the project into a closed source for-profit product.
well we don't know exactly how involved Gabe Newell is with the actual running of the company now a days or how do they going about their governance.
From what I see it seems like the culture of the company is shared between the leadership roles so it might be possible for the company to continue doing as it has been doing after Gabe.
I think the people at valve are smart and they understand their business and the company very well and that this issue is being taken seriously too.
Good governance exists, it's just that for most companies there's not really an interest in having that because it gets in the way of personal interests of people that are already entrenched in power.