what might happen if all the protist on earth died?

Answer 1

Most animal life forms would probably also die, which could including us. Protists provide food and oxygen for many animals, and any animal above them in the food chain would be affected enormously.

We'd also have one humongous clean-up problem.

Answer 2

it would affect marine life (algae) which has a ripple effect and affect us too.. fishes would have no food to eat or shleter to hide in and this would contrtibute to their death and so on.. other protists eat decayed materials to and recycle them