Beautiful topic, once again. Thank you everyone. Just came to my mind what Ramana wrote to her mother, who was begging him to come back home from Arunachala:
Whatever is destined not to happen will not happen, try as you may. Whatever is destined to happen will happen, do what you may to prevent it. This is certain. The best course, therefore, is to remain silent.
We do have free will. However, when driven by our samskaras our trajectory is determined largely by them, in the same way as a stone thrown from a sling will have a predictable trajectory. That's one sense of "what has to happen...". The past will determine the present.
When we abide in silence, we are free from the interference of samskaras. Then we will ask "what does this situation require?" and we will act according to the dharma. I see it as another kind of "what has to happen will happen".