I don't believe LE has any info on whether Isabel is dead or alive-how could they? We have heard this answer in so many cases (no reason to believe he/she is deceased.) We heard it about Kyron for months on end, until they stopped talking about him at all, even when they were searching woods and fields and examining animal bones...
Without a crime scene to show injury, I don't think LE ever can know the status of the person. But you never hear LE say they believe someone is dead, IMO, unless they have some evidence that points to it, or at least a history of violence, ie. Jhessye (spelling/sorry).
JMO