This all depends on the people, really. In RL games I've seen times where the last 3-4 people in a tournament would just agree to split the pot according to estimated ratios. Some will split evenly. Sometimes people get infuriated at the idea of it.
That's a chop. All the remaining players can agree to whatever split they like, so long as there isn't a rule against it.
If they waited for the fourth player to go out of the room to take a whizz and then agreed to screw him over and split the money between themselves, that would be collusion and cheating.