A car can be driven with only 3 sets of brakes.
However it's best to make sure all 4 sets of brakes are working to provide the most stopping power.
I have had to block off one brake line on my trucks rear wheel cylinder before when I was on a road trip and the rear wheel cylinder on the passenger side was leaking.
I had to remove the brake line and cap the line off and then bleed the brakes again and then I was able to drive the rest of the 100 miles until I was able to get to an auto parts store and get a new wheel cylinder.
I replaced both wheel cylinders at the same time because the other one was old as well and could have leaked.
So if you have to drive with only 3 brakes then you can but you really shouldn't unless absolutely necessary.
Your brakes are very important to your safety, your families safety and other peoples safety around you.
So don't cheap out on brakes and get them fixed.