Sam Altman is not some AI genius and is more like a sales guy , this is not gonna make much difference. Most researchers at OpenAI would be reluctant to follow Sam to MS as its a massive downgrade in terms of salary, politics and culture. Even assuming they leave (which is a big assumption), IIya is more than capable of finding replacements due to his academic connections and reputation. Researcher like IIya are the main reason OpenAI is what it is.
Not to mention, MSR itself once had an awesome reputation like OpenAI, and Satya gutted them with his short-termism and politics, which led to mass exodus of AI researchers and engineers. Unless he suddenly increased the pay, improved the culture overnight, no way they can attract and retain talents