That's a simplistic take on a very complex equation. You're simply looking at the gun deaths that would be prevented by the removal of guns from the situation, and assuming that's the end of it. It wouldn't be. You also have to consider that demand for illegal goods leads to black markets. Some people will have guns, legal or not. Who will those people be?
You also have to consider the lives saved by guns. Scientists estimate anywhere from 100K to 350K defensive uses of guns each year. Not every use saved a life, but the number that did is undoubtedly non-zero.
Finally, once you do all that math, you can't simply look at which number is bigger. There's a qualitative aspect here, too. Most gun deaths are suicides. But why should gun policy favor the potential suicide over the potential self-defense? I would argue the tie goes to the runner, in this case, in favor of more freedom and more choice. If policy A results in 10 lives saved by self-defense, and policy b results in 10 prevented suicides, I'm going with policy A, and looking for another way to attack the suicide problem.
Fair. Has such a study been conducted?
And that doesn't address the individual level. On an individual level, it is mostly likely irrational for your average person to be purchasing a gun for reason of personal safety.