I imagine his gambling debts catching up with him might cause Wickham to make himself scarce. One reason for his flight. People took "debts of honour very seriously."

Another question. Did Wickham know of the entail? I don't recall it coming up in any of his conversations. It might be common knowledge around the area, but would he have bothered to ask "is there any reason why the Bennet's aren't as well off as they seem?" (This while setting his sights on Elizabeth.)

You'd think Lydia would have let it slip at some point (at least before they "eloped"). However, I suspect her family's future financial uncertainty rarely enters her head. At most, she probably simply thinks her father is rather tight-fisted.

More versed readers can correct me, but is it possible Wickham didn't realize how little he was getting out of the deal?