The mega-billionaire Bill Gates, even after all he's already donated, and after his divorce, is still worth $113 billion, and has pledged that almost all of it will go to charity at or before his death.
It is a fair assumption that most of that will go to the Bill and Melinda Gates Foundation.
Mega-billionaire Warren Buffet, a friend of Bill Gates, has pledged likewise that 99% his $90 billion wealth will go to charity, with at least $55 billion going to Gates Foundation.
(The donations will be in the form of Bill Gate's Microsoft stock and Warren Buffet's Berkshire Hathaway stock, which may be worth even more in the future)
So if Bill Gates was kicked off the foundation in a coup, it is very likely the Foundation would lose out on $150+ billion in expected future donations.
Additionally, as it has Gate's name on it, and is funded by many of the wealthy people Bill Gates rubs shoulders with, it's likely the loss of future donations would exceed $200 billion.
The Gates Foundation currently has an endowment of $67 billion,
Bill Gates is 68 years old, and not in the best of health. In makes more sense to simply wait him out, and then there's no controversy, the organization you'd be in charge of would be sitting on a vastly larger treasure chest (triple or quadruple the size, from $67 billion to a likely $250 billion), and no fear of revolts from loyal employees, or retaliatory lawsuits from one of the worlds richest men.