With regards to the OP's question, let's remember that I don't believe it was ever stated that Picard was going to force the colonists to leave. Right up until the end when he destroyed the aquaduct, Data was trying methods of persuasion. There's no indication that he would have forcibly removed them in the end, had they failed to agree.
Right. The whole dilemma driving the story was that if Data was unable to persuade the colonists to leave, they would die. Dramatically, the point of the story was to test Data in a leadership situation, a crisis where he had to persuade humans to trust and follow him -- kinda like "The Galileo Seven" was for Spock. That doesn't work unless the colonists' survival depends entirely on his own ability to convince them to cooperate.
Let's remember, after all, that the reason Data was alone down there is that he was the only person other than the colonists who could survive the hyperonic radiation on the planet. So nobody else could
have come down to forcibly evacuate the colonists. Either they did it themselves or nobody did.