Your controller controls your professional DJ software, period. And all of your live DJ skills can still be performed without it.
Midi units, or even time code vinyls, still spin the same digital music files on your hard drive. And midi controllers are simply a set of buttons and knobs that are mapped to the various functions of your DJ software.
Do you know what other buttons are mapped to the various functions of your DJ software? That's right, the ones on your computer keyboard.
By going into the settings of your DJ software, you can learn which keys are mapped to what functions, and still perform at the top of your game by using a combination of key strokes and mouse clicks.
As with anything else, this will take practice. One of the biggest challenges in using computer-key strokes particularly, can be making sure the cursor isn't flashing in your software's search box to look up songs. If it is, you might hit P for play, and just end up typing a P in your search box.
Just remember that live & traditional DJ mixers are not midi-compatible, so they won't visually control your DJ software. But this is another alternative to using your computer's headphone jack for the master output, and your adapter for your headset (or vice versa).
If you're a DJ who believes in having multiple back up solutions, then at the very least, you now have some great ones. Backing up your mouse & USB adapter or headset is much less expensive, and will definitely save you from having to buy another controller or two, in case of emergencies.
On a side note, for many reasons, my own personal preference is to DJ with my computer's mouse and keyboard. I have used quite a few controllers in my career, and just find them unnecessarily adding extra steps. Especially for the style of mixing I do, which has always impressed my clients and their guests, controller or not.
On another side note, I have seen fellow DJs doing what I personally feel is a great disservice to their clients, by bringing some of the biggest Freudian compensations of a controller, and not even putting it to proper use. They only have it there for show, and are not even doing any mixing.
So again, no matter what kind of equipment you use, Practice! Practice! Practice! And rock your clients' events correctly.