What would happen if radium never existed?

Well it's hard to say what would happen since I have no psychic ability but there may or may not be a significant change on earth since Radium isn't very abundant anyways and it has very few practical uses. All I can think of is that there would be one less element on the periodic table and the pattern of the periodic table would have been somewhat broken if nothing with the properties of Radium existed to fill that space on the periodic table. Perhaps a few people wouldn't have died from radiation emitted from Radium since it was formerly used in watches, clocks and aircraft switches. Radium is commonly used in cancer treatment so more people suffering from cancer might have died unless they turned to some other sort radioactive element to use in cancer treatment. A few people wouldn't be famous for their discoveries such as Marie Curie who discovered the element Radium and others who found practical uses for it. A lot could change or there could be very little change. It's very hard to say.

What would happen if gravity never existed?

or if ratio of a circle circumference and its radius is not pi?

What about what would happen if the laws of physics do not include the conservation of mass and energy (1st law of thermodynamics)?

The answer is.....

That we will not be "here", natural law do not have a reason to exist but if they don't its quite possible that we couldn't exist!