They have shown its a wildly successful model. They would be very crazy if they changed it, and it would make them vulnerable to Epic and the Windows store. It's more likely that your OS/ hardware will change in a way that isn't supported by an old game.

Unfortunately, "this is a wildly successful model that prints money for us with almost no upkeep required" has historically not been a bulletproof argument when new management comes in and wants to prove themselves. Human beings are not necessarily rational and the kinds of people that tend to rise to the top of large corporations don't necessarily have the best interests of customers or the business itself in mind.

That being said, I believe that Gabe is taking his "succession planning" seriously, so I'd be fairly optimistic for the next decade at least.