They don't have to be board members to fight. The 51% shareholders are clearly wronged here in my view if MSFT just hires all of OpenAI staff AND takes the existing models and trade secrets.
Again, you should check who those 51% are. If you don't know who they are and what their relationship with Microsoft and the various board members is then you probably won't understand why your comments on this subject don't track.
Hint: the 51% are more likely to go after the board than that they are going to go after Microsoft because the board action is what precipitated this whole mess.
Microsoft is just - conveniently - picking up the pieces and periodically drops hints about what they'll do if anybody gets in their way of doing that.