Reduced to 0 HP and then?

[Destil]

But they don't actually need that. If you have initiative of 16 and I have initiative of 14, my actions aren't reactions to your actions. They just take place after yours in the sequence of events.

Unless otherwise stated free actions can be taken at any point, not just during your own turn.

As far as OP: I think the wording I would treat this as would be 'No action.' meaning it happens and there's nothing that can be done to stop it.