I subscribe to the "make it fresh the day of the event" theory but a buddy of mine has asked me to provide pre-cooked brisket so he can warm it up a week later for a family get-together.
I was a little suspect at first if the quality would hold up but he swears it tastes just like it was off the smoker.
Basically, cook the brisket as you normally would. After resting, wrap it up tight in some foil and put it in a container for freezing. Toss it in the freezer. On the day of the event, pull it out and while whole and still wrapped, put it in the oven and let it come up to temp. It'll retain all that moisture. Once back up to a safe temp, rest, slice, enjoy.
Another option, if you have one available, is to vacuum-seal the whole brisket. Then you can sous-vide it in a pot of boiling water when its time.