“Microsoft has assured us that there are positions for all OpenAl employees at this new subsidiary should we choose to join.”
Microsoft can absorb all the employees and switch them into the new AI subsidiary which basically is an acqui-hire without buying out everyone else's shares and making a new DeepMind / OpenAI research division inside of the company.
So all along it was a long winded side-step into having a new AI division without all the regulatory headaches of a formal acquisition.
Microsoft is a substantial shareholder (49%) in that for-profit subsidiary, so the value of Microsoft's asset has presumably reduced due to OpenAI's board decisions.
OpenAI's board decisions which resulted in these events appear to have been improperly conducted: Two of the board's members weren't aware of its deliberations, or the outcome until the last minute, notably the chair of the board. A board's decisions have legal weight because they are collective. It's allowed to patch them up after if the board agrees, for people to take breaks, etc. But if some directors intentionally excluded other directors from such a major decision (and formal deliberations), affecting the value and future of the company, that leaves the board's decision open to legal challenges.
Hypothetically Microsoft could sue and offer to settle. Then OpenAI might not have enough funds if it would lose, so might have sell shares in the for-profit subsidiary, or transfer them. Microsoft only needs about 2% more to become majority shareholder of the for-profit subsidiary, which runs ChatGPT sevices.