Sell their tesla shares, and the sooner the better

A majority of investors could get together and replace the board.

Otherwise not much. Part of the risk in investing is that you might invest in a company with shitty management. If you made a bad investment (except in very extreme cases which this probably doesnt cross the line into) that is your fault. Investing is not the same thing as free money.

Sell earlier than later?

Sell it now and minimize the loss.

Probably best to sell and buy BYD or Rivian stocks if you're betting on EVs

They can celebrate a couple of decades of success. Tesla won, it truly changed the world - EV's are everywhere now. The shareholders helped build that, and even if Tesla is now dying - it meant they made a difference.

other than sell? it's still not clear if they even have director independence.

Musk's job is to make investors money. The moment he stops doing that, he's dead weight.