I don't know what the solve rate is for abductions, but I suspect it's quite low. He's dealing with the high likelihood that either she died before she left the house or died shortly afterwards, and her body was left somewhere. This is a vast area with lots of places to leave a body. My opinion is that her body will never be found. I'm sorry to say that, because I know that many here are aching for her return.
If he suspects this, or in fact knows this, he's looking at years of unrewarding, dogged work, chasing thousands of leads. This is the rest of his career frankly and it will never leave him. His entire career will be judged, harshly, by the lack of results and failure to deliver an outcome people want. Who knows if he'll be able to identify suspects who can be prosecuted.
I'm sure it's not a case that he welcomed or wanted. It's not going be a positive outcome or a satisfying end to his career. It's going to be depressing and demoralizing for all.