You definitely cannot freeze cooked barbecue brisket and bring it back to life at adequate commercial quality. You can freeze raw brisket, but that doesn't solve the core problem of serving barbecue brisket, which is that it takes so long to cook that you have to either be really good at predicting your turnover or close up early when you run out.
Long story short: freezing brisket, not a great plan.
You certainly can freeze barbecued brisket and bring it back to life in great shape——I've done it plenty of times. It took a lot of trial and error, but it's not impossible. I'm not cooking a 18 hour brisket just to eat a quarter pound of it and toss the rest.
Long story short: freezing brisket, not a great plan.