The old shareholders cannot do anything. His new investors are like a dozen on billionaires who own pretty big pieces.

They don't have an equity stake in the company

They are creditors, though. The terms of the loans are not public, but usually being a creditor provides more leverage than a minority equity stake.

Yes they do. Not the banks. The billionaires who came in as junior partners. Larry Ellison is supposed to be in for a billion. a16z and Andreessen personally are reported to have equity investments. One of the Binance founders, or Binance as a company is supposed to have hundreds of millions of equity. The very large Saudi investor (I don't know if it was an individual or the sovereign wealth fund) when Twitter was public is still involved.

There are a few publicly known partners, and a few who got turned away. They have equity.

My limited experience is that people with money can still influence companies, even if there aren't formal paths. Share owners still have influence.

And people who lend money typically have contracts and the ability to seize assets if they don't get paid. (I have no idea what the $13B of loans looked like, but can't imagine they were personal, non-recourse loans.)