This narrative doesn’t make any sense. Microsoft was blindsided and (like everyone else) had no idea Sam was getting fired until a couple days ago. The reason they hired him quickly is because Microsoft was desperate to show the world they had retained open AI’s talent prior to the market opening on Monday.
To entertain your theory, Let’s say they were planning on hiring him prior to that firing. If that was the case, why is everybody so upset that Sam got fired, and why is he working so hard to try to get reinstated to a role that he was about to leave anyway?