No company will ever do that. Even if they did, no one on the planet should expect it to play out as described. The whole anti-DRM position is based on the fact promises aren't worth a damn thing.
Publicly announced succession plans happen fairly regularly, especially for a company as stable as Valve. Tim Cook is 65 and just did so for Apple. The announcement of Ternus was hardly a bolt from the blue, either. Gabe is 63, and there is little to no indications.
> No company will ever do that
Ignoring how many counter examples of this there are, why wouldn't Gaben do this given that he's majority owner of the company? He can do whatever he wants.