They'll be made abroad and smuggled. Guaranteed. And we will not be able to stop it - just look how well the War on Drugs has worked in curtailing smuggled drugs.
I can tell you from personal experience it is a LOT easier to buy assault rifles now, post ban, than it was during the ban. Back then you had to find someone with a pre-ban assault rifle that wanted to sell it and didn't want a lot. There were not a lot of "smuggled" assault rifles on the market.
I'd like to go back to those days. Also, with pending legislation making background checks mandatory for even private sales, all we're missing is a gun registry -- once we have that, we can tell who is selling them illegally. How often do you see people buying cars on the blackmarket that have been smuggled in and have no ownership trail? Not many. More common for blackmarket cars to just be chopped up for parts.
Maybe some day we'll achieve that with guns, but probably not until the NRA loses relevance in congress.