One thing to keep in mind is that Valve is fully private so Gabe can not just be replaced by some random person by a board of directors like in other companies.
He probably already has a will set up that details how ownership should be transferred.
It is, but I'm not sure why that's relevant? xdertz's point wasn't, "Valve is private and therefore it engages in ethical consumer practices"; the point was "Valve engages in relatively ethical practices and because it's private, the board can't replace Gabe with a CEO who would engage in more unethical practices".
Not sure if this is relevant, but I have read reports[1] that Tencent currently holds a 28% stake in Epic Games. So private, but with unknown levels of ownership.
He probably already has a will set up that details how ownership should be transferred.