If the Patriots were to keep Collins on the team for the rest of the season it would likely cause his teammates to stop doing their jobs in order to cover for Collins' incorrect positioning. So now we would have multiple players adlibbing because a teammate may vary from the script.
Now, think about the times that Brady has struggled at quarterback. It always comes down to him not being able to "trust" his receivers. Once he has trust with a guy it's like clockwork. The same thing has to be happening on the defensive side of the ball. Everyone needs to trust each other for the game plan to work.
For a quick analogy of what can happen when adjustments are made on the fly, I'll take you back about 30 years to a cheerleading competition my sister was participating in. Leading up to the night of the competition, the girl who was supposed to fall off the top of the pyramid into her teammates outstretched arms wasn't jumping out far enough. Well, come the night of the competition, she jumped out further than she was in practice. Meanwhile, the teammates who were tasked with catching her moved closer to the pyramid. Next up was a trip in an ambulance after an almost free fall to the gymnasium floor.