If I report a phone as lost/stolen AFTER the thief gets a chance to put a sim card in, would it lock the phone just like that?

Got my iPhone SE stolen a few days ago, and Koodo is supposedly calling me tomorrow to ask if I want to report it as stolen. Is it possible that the thief is able get away with this?

Added (1). Also if they manage to unlock the carrier somehow?

Mbbn

They would likely try to reset it & you can't get far without the Apple ID & password, if that's any consolation.