Great post Damian. You highlight a good aspect of agency here too--the choice to do nothing. It can work great when the result of the character's inaction have an impact on him directly, like your example of the slain father.

It can work if the result of inaction doesn't effect the character--like walking down the street and choosing not to interfere when an old woman's purse is being snatched--but it's only effective in showing your reader the type of person your character is, which is fine at times, of course. But if you're going for more, then imagine the direct impact the character's agency will have in tgat situation when he finds out that was his own Grandmother. Effective agency drives the character's arc.

An excellent topic you've touched on that writers should always keep in mind.