Not reading 142 pages, so sorry if it's already been said, and haven't been following the story too much...
My guess is a deal gone wrong. Maybe also connected to a Rolex going missing.
He's been made aware that he's done for and decides it's better to "disappear".
Reasons:
Why walk away from a bus stop that was due in 10 mins = makes no sense
Why wonder off the main road, even if you don't know which way to go = even the wrong way just keeps you on the bus route
Why facetime somebody to tell them that your lost, thirsty and only have 1 bar of battery = a text would achieve the same result and save battery
The last phone "ping" locates the phone down a steep ravine way off the track = thrown there to hint he has fell
So while i could believe it's all an accident, i think it is more likely deliberate.
I feel there is a chance he has come to harm at somebody's else's hands for a bad deal/theft. I think it most likely he is in hiding at a friends place, still on the island.
I bet the plan was to lie low for some time and try and return home on the quiet.
Not the brightest idea because of the media attention. But these people tend not to be the brightest, and it is probably a unplanned panic decision anyway.