It's a presumption that they would have killed him or his family or both. If Siri was, in fact, elected -- as this documentary suggests -- he should have accepted his duty and left the rest to God rather than yield to natural considerations, knowing the enemies of God were about to seize control of the Church should he refuse.
He and/or his family would have been martyrs. Nothing wrong with that...! That's how Catholics think.
I’m not judging him. I do know a distant young relative. I do know that there could be more to the story. I don’t know if/who he appointed and who may have followed him.