What you are saying seems to me to be completely groundless in every dimension.
Also: I did not state the antithesis "Satya Nadella had nothing to do with MSFT adding $850b to their market cap". I'm just stating "It's not true that MSFT adding $850b to their market cap is attributable solely to Nadella".
I like your point about the board though, and I wonder how the MSFT board specifically feels about Nadella.
It's trivial for a CEO to issue a puff piece as a marketing tool. Steve Jobs tried to advertise himself next to Ghandi. Assigning credit is a difficult game. Studies show people over and under assign credit. The best/most realistic crediting of work to successful performance ratio ended up with the team crediting to one another something like 115% over how much work was actually done.
Debating over blame and credit is mostly a waste of time, even though people fundamentally need positive feedback for good work and negative feedback for bad work. It's mostly used politically in big corps and that's a big void I try to stay away from.
What would happen? Things would function. They'd probably be fine for the first couple months, and they might even pass their first quarterly earnings without anyone noticing he's gone. If the department heads all were quiet and didn't notify the shareholders, things would seem completely fine.
But then the next quarter comes up. Money shifts around a little bit creating a small deficiency here, and a surplus over there. Department heads start to assist each other towards shared goals which may be detrimental to other departments.
Tribalism starts to take hold. Each department head is now their own top dog, and some will start to breed a culture within their areas where they believe they are absolutely more critical than other areas. Some individuals may start to actively sabotage the other departments if they feel it serves to benefit their own dept.
Without a CEO, you no longer have a company, you have a community of companies that are in direct competition with each other.
This doesn't mean the individuals within a company are unimportant. They get plenty of recognition within their own circles, but when you're talking about money, there's a reason the CEO is the focal point.