JFK-LAS is a one way market. If you know you are going to go for sure, you can buy the JFK-LAS flight now and wait on the return.

B/H is a pricey fare -- unlikely you will lose out if you wait. Although not perfect, look at the seatmap. If the entire plane is empty, they're probably just holding the cheaper inventory

Set up an expertflyer alert for your return flight for the cheaper inventory....oh wait - nevermind...thanks DL