Attrition will probably take your gun. Over time, there won't be that many working weapons and certainly not enough to fuel the black market in the current manner.
Again, not the point. The question is not whether a gun ban would be effective, the question is whether one is a realistic option.
I have a friend with a springfield 1898 that probably served in the spanish american war. It's no show piece and it fires fine... I think he hunts elk with it.