As long as the crockpot is on keeping the soup warm or hot the soup can remain or sit in the crockpot for a few days before it overcooks.
I have kept soup warming in a crockpot for 2 days before as I made a big crockpot of soup and had too much to eat in just one day.
So I kept it warm in the crockpot because I had no room in the refrigerator for it.
I kept the crockpot on the warm setting and then finished the soup within a few days and it was okay.
However once you shut the crockpot off then the soup will only be good for up to 2 hours before it starts going bad and growing bacteria.
If you leave the soup in the crockpot longer than 2 hours then it's likely going bad and should be thrown out.
But if you refrigerate it within those 2 hours it will be safe to eat for up to 5 to 6 days.