Lurker no longer, first time poster.
From what I've seen and read of BL and this case, I think he's dead by his own hand in the Carlton Reserve. I don't see an individual who could outwit LE, dodging around the trails of America or hiding out one step ahead.
Right after killing Gabby, he may have tried in some way to create a story and alibi whereby he wasn't at the scene for a few days. Hike to Colter Bay, return to Spread Creek, report Gabby missing and take his chances. Reconsidering, he knew this wouldn't work - he'd be the prime suspect from the outset and at the mercy of the authorities.
The stark reality - fall into the hands of LE, it's a life in prison for him. Fresh air, outdoor loving BL was never going to countenance that as an outcome. The fact that he took the van and bolted for home, stealing Gabby's money on the way, was akin to an admission of guilt and that his prospects were bleak.
Back home, I think he knew what he was going to do. Have a last taste of his old life until LE closed in as he knew they would. He might have thought about going on the run or into hiding. But what are the chances that might work? It would be a miserable existence likely doomed to failure soon enough.
To my thinking if he was going to make a run for it, he would not have waited around for thirteen days. The sooner he got out of there the better and before Gabby's body was found, and he did not know when that would be. He got thirteen days before heading to Carlton Reserve for the last time.
Finding any remains or evidence in that reserve is a hit and miss affair. Substantial areas of it make systematic feet on the ground searching problematic. I don't think helicopters or drones can effectively scan the really densely grown areas.
MOO