They climb into the back of the truck. They go off with the person who recruits them.

The Seva Foundation was started by a group of alumni of the smallpox eradication program who, having climbed the highest mountain, tasted the elixir of the success of eradicating a disease, wanted to do it again.

It was precisely these people, by all accounts, who skillfully climbed onto the roof (maybe having set fire to a couple of rooms below, just to be sure).