Everyone is replaceable, the only good thing you can do is be a good person, so atleast you are remembered behind your back.
Same is for a software developer, doctor, businessman, CXO, CA etc.
Curing cancer or solving world hunger, let’s face that, even if we cure cancer, that treatment will be way commoditised and ultimately if will be corporations that will be making money, not the researchers who has cured cancer, he will win a nobel prize, though.
The only good thought is, not let success get into your head, varna your nobel idea or you, both will be mocked to hell (cough - bhavesh agarwal - ola)