I wonder where this 15% figure comes from. All the research I can find estimates the probability for these disorders at around 2-4% for first degree cousins. This is about the same as becoming a mother at 40 with a non-related man.
The article only talks about some NHS training documents and is very opinionated in style. Smells like a snappy headline about a controversial topic was more important than proper research.
I can‘t find the specific video where it came up, but I remember Chet Faliszek, who worked at Valve from 2005 to 2017, mentioning, that Gaben‘s death is something that has been planned for and won‘t be as much of an issue for Valve as people might think.
It‘s of course in no way guaranteed to work out in the end, I don‘t know the specifics of the plans or if everyone‘s going to go along with them. But seeing how well Valve is doing and also how little Gaben actually seems to steer the company, I‘m somewhat optimistic that it‘ll be fine after his passing. Not optimistic enough not to have my most beloved Steam games backed up somewhere, of course, but still somewhat optimistic.