I gotta agree with Sylux on this one. Maybe he intentionally leads the crew into a trap to buy him some alone time with the monies, or maybe he just buggers off with as much as he can carry the next time the crew is under attack. Third option is that maybe the entire crew go after something stupidly powerful and expensive, and Zach dissapears after nabbing it first, not wanting to share it. Maybe Annah told him he got really drunk and married Jang.