Do sports books ever buy back their long bets before they are resolved? If, when the season started, you had bought a ticket for the Montreal Canadiens to win the Stanley cup, could you have sold that back before the final series started? Presumably, it would be worth more, as Montreal had made the finals.
Yes, they do. It's called “cash-out.” It's much more popular in other places around the world than it is in the States, but it's starting to catch on here. Still, as far as we can tell, it's available only at online sports books. No brick and mortars we know of offer it. As of this writing, it's offered by DraftKings, FanDuel, SugarHouse, and 888.
You'll see the cash-out option, and the current price of the ticket, in the active-bets area of your account online. You click the cash-out box and your funds are, in most cases, instantaneously returned to your account.
Various cash-out options are available for single games (both money line and pointspread), parlays, and futures bets. In the case of the Canadiens, the cash-out option would have been good until futures bets on the Stanley Cup closed out.
The price, of course, depends on the projected outcome. Going into the Stanley Cup this year, with the Tampa Bay Lightning pretty heavily favored, cash-out was probably a good thing to consider, though since the Canadiens were a major long shot, holding out would have paid off handsomely in a massive upset.