If Vince owns 80% of WWE shares like has been stated, that means he would end up owning 80% of the 49% WWE shareholders would have. Which means he would own 39.2% of total shares of the new company.
Not enough to squash something all on his own, but if whatever they are voting on needs more than just simple majority - say like needing 60% approval - he could be in a pretty powerful position because just about everyone else would have to be on the same page opposed to him to get it done.
If it's simple majority, it won't matter what he wants, Endeavor will have 51% of shares so they'll get what they want.
But alas I admit I don't know what voting requirements are for stuff on the board. Not something I ever really cared to know or learn about.