Isn't Microsoft in breach of contract here? Not by the word (parties hadn't forseen such event, and so there won't be anything about this explicity in the contract). But one could argue that MS isn't acting in good faith and acting counter to the purpose of the agreement with OpenAI.

The argument would go something like this:

MS were contractually obliged to assist OpenAI in their mission. OpenAI fired Altman for what they say is hindering their mission. If MS now hires Altman and gives him the tools he needs, MS is positioning itself as an opponent to OpenAI and its mission.