Very debatable. It takes a lot of effort to kill somebody without using a gun; to a large extent crimes of passion would end in injury rather than death.
It is very debatable because "large extent' is subjective terminology. And I think it's true that certain "crimes of passion" would be much less likely to result in death.
At the same time, contemplate things like gang-related homicides. Say a drug cartel decides someone has to be eliminated. The fact that guns aren't available aren't going to stop them.
Like I said, the number would be reduced by some extent. But it wouldn't be a situation in which every murder that would be committed with a firearm under current circumstances would not be committed if guns weren't available. Frankly, I think that only a
minority of those murders would be prevented. And the United States would still have a substantially higher murder rate than, say, Australia.
Remember: The largest mass murder in US history was committed with two airliners and the second largest was committed with a truck loaded with fertilizer.