In other Chiyuvei Misah we don’t intervene (although we are Matzil Be’Evarim IIRC). The fact that we kill a Rodef of murder or Arayos is either because he is presently a Rodef or it is about prevention. This is a famous sugya. Our Shayla might depend on this, too. He will definitely kill but not necessarily is he an active Rodef. So, if Rodef is about him deserving Misah then there is the requirement of Din Rodef. But if it is about prevention a definite crime it should apply here, too.
This is not iron-clad, of course. There is room for each view to hold either way.