If it turns out that his data are good and his methods are sound would it make the tiniest bit of difference to anyone's opinion?
For me it wouldn't make a difference because rights are just that, rights.
We have the right to travel, but thousands of people die in travel related accidents. That doesn't mean that I would support the suspension of my right to travel because it might save lives.
We have the right to speak, but people's feelings are often hurt by the words of others. That doesn't mean that I would support the suspension of the right to speak just to save the feelings of those who might not like what others say.
In addition, from the practical perspective
I am safer because I own guns, so why should I have to sacrifice my safety for the safety of others (most of those others likely being criminals).
There is also an axiom among statisticians that is often forgotten;
"Correlation does not equal cause." So just because areas in the country where there are more guns there is more murder may not have anything to do with the guns.
If some study said
"States with higher rates of consumption of carrots have higher murder rates." would we then conclude that carrots cause murder?
And finally, assuming this study isn't flawed (which I expect we'll find out it is ... this pattern repeats itself too often) but IF we find the data is correct, how do we reconcile it with the studies that show that murder rates are also higher in areas with tighter gun control laws?
On a side note, one of the flaws I can see is looking at the issue from a Statewide position. Looking at my home state of Colorado, I can bet you that outside of Denver the rate of firearm ownership goes up, some parts of the state considerably, but Denver (where firearm ownership is less per capita than the rest of the state) has the highest murder rate. So when you have an urban area that skews your murder stats when compared to the peaceful suburban and rural areas (where the guns actually are) you create the false impression that the number of guns owned is what is causing the high crime (because overall there are a LOT of guns in the state, and a lot of murder in a concentrated area that also happens to have a lower rate of firearm ownership).
Other states are likely the same. Lots of guns in rural Illinois, plus lots of murder in Chicago (where most of the guns are not). Lots of guns in rural Texas, but lots of murder in Houston (where most of the guns are not).
Anyway, that was probably somewhat rambling but I'm typing it while doing a dozen other things