The trouble with any "ban on guns" is that it would do nothing to eliminate the millions of guns already in circulation. Unless that issue is also take care of in some way, then banning guns will do little to affect homicides in the short term.
However, almost every other civilized country in the world has proven that a society without guns tends to be a society which has a lot less homicides. Violence will never disappear, and assault will never magically stop, however having access to a gun elevates an argument, or an assault, or a domestic dispute, into a potentially life threatening situation Likewise, a person who attempts suicide using a gun is 80% likely to kill themselves, whereas virtually all other suicide attempts have (on average) only about a 20% success rate. Hence access to a gun is much more likely to turn a suicide attempt into death.
Likewise, a moment of road rage, or drunken stupidity, seems to regularly turn a moment of anger into a shooting.
So Yes, a gun ban would almost certainly reduce homicide attempt rate as has been shown worldwide, however in America it would be impossible to implement anyway.