Yes, at a certain level of play, one must continuously play just to maintain the fine edge. However, the top pros don't just play to maintain where they are, they practice to get even better than they currently are.
But, to be sure, a pro will come home from a tournament with a notebook filled with shots he missed (even almost missed). They will set that shot up and shoot it again and again and again until it become rote muscle memory. perhaps the shot was a safety where just a tad too much energy was involved and lead to a "complete sellout". These shots will be repeated until the touch is developed, ingrained, commited to muscle memory, and become part of the practice regiminie for several months.
The notebook will also contain patterns the opponent shot. The pro will set these patterns up, and consider whether there is a glimer of advantage to how the opponent played the table rather than how he would have played the table position. And whether there is a still better way to do it (than either saw durring actual play).
The notebook will recoder the games/matches played, the players played, and observations about the player and how they played, looked, facial expressions, posture while sitting,... all of which gets lobbed into a database so when the next tournament comes around, the shooter can read up on who they will be playing, how to frustrate them, what shots they like and how to prevent giving them those shots.
The ones who want to stay on top, will be found practicing somewhere between 4 and 8 hours a day, every day; where each shot is given the absolute full concentration level of the "6-6 hill-hill last shot to win" shot.