If it goes out of control at least 50% of the world will become infected, and that will cause more deaths than WW1 and WW2 combined.
About 10-15% of people who get it need ICU.
If 3.5 billion people get it, with 10% needing ICU, I think the world has about 1 million ICU? Most people who need ICU wont be able to get it.
Now because 350 million people wont need to be ICU'd at the same time, it'll be over the course of a year or 2, so maybe 50 million out of the 350 million who need an ICU will get it, and thats probably guessing way over it, so still, you'll have hundreds of millions of people who need ICU who can't get it, a lot of them will die.
This is where the "more deaths than WW1 and WW2 combined" come into play
This will all take place before a vaccine is ready for mass distribution.