Nope, that's part of the plan. Sure you can keep yours. You just can't get another one, and it becomes a hassle to sell yours. With availability strictly limited, market prices for used items rise to the point they're practically off the market.
The most successful bans don't get interesting. They just make things excessively expensive and dull.
After they thoroughly decimate the civilian firearm market with bans like this they'll get greedier and scheme up elaborate registration schemes that lead to eventual attempts at confiscation in gradual increments. For now though I plan on buying much more ammunition before they target that as well. If I can't buy another "assault weapon" I'm going to make sure I can keeping shooting what I have.
And of course you won't be able to buy an replacement magazines, made after the ban at least, without which you've got a single shot and/or expensive club.