First, very few took the poison willingly. Most (the majority) were either held down and injected, and killed that way. The tiny few that took it willingly either had to watch their children die, were threatened or felt no way out. Armed guards lined the pavilion.
This was in no way a mass suicide. People did not line up and drink the poison to die in a "revolutionary" suicidal way. People were screaming, frothing at the mouth, holding their stomachs doubled over in pain after they were either forced to drink or were injected.
There were at least two people that probably (we don't know for sure) drank without question, due to their previous problems with suicidal tendencies before Jonestown. We figure they probably in fact drank it first.
It seems there probably would have been an incident, whether Leo Ryan was killed or not. The facts show that Dr. Larry Schaact wanted to test the poison on pigs in the Jonestown piggery months before it all happened. There was another memo that asked "what do we do with those that don't wish to die?" This was also dated months before any of the murders took place. This was planned long before any of the killing of people began.