That isn't really a thing here anyway. Small shopkeepers just don't keep a gun behind the counter. It's illegal.More likely, it will _increase_ as the criminals lose fear of a homeowner or small shopkeeper shooting his arm off.
About 6% of the population has a gun license but estimates of about 11% actually own a gun. Probably a lot of them are "dad's old hunting rifle" they still have or that they inherited sort of thing because you only needed a license for about 20 years. In the far north almost all families have a rifle for hunting.
We do have burglary and the very rare home invasion but I can't think of ANY time I've read of Canadian homeowner using a gun to shoot a criminal breaking into their house.
I read a study some time ago about "why do Canadians own guns?" Hunting was the reason something like 89% of the people gave. About 5 or 6% said "self defense".
So if you make it harder and more costly to get a pistol, it doesn't mean criminals won't have them. It just means they will be less likely to have them. Which is a good thing.