I'll honestly be shocked if Microsoft doesn't buy Valve in day for Steam. Obviously current ownership would be against it, even with Nadella, but one day it just feels like a guarantee.
He and Michael Harrington founded Valve a year afterwards. I asked Gabe over email if it was because it was the 1 year anniversary of Windows 95 launch but he said Valve was actually founded on his wedding day.
That's never going to happen, at least not while he's alive.