What if when the child becomes an adult, questions our decision of choosing Open Learning?

Two important points here – Any child can actually question any decision of their parents at any point of their life. That in itself does not mean that we need to take all right or safe decisions, because perhaps any decisions which might look right or safe can be questioned and seen as otherwise later. You see, the child can also question why you sent them to school and anto allowed to do open learning!
Second in open learning we as parents interact with the child on a daily basis, constantly reviewing other all the decisions and plans and executions, including the decision to do pen learning. So the children are as much part of the decision making and hence no question of them questioning us later.