The Islanders will be back in Brooklyn at some point, I have no doubt about that. My gut tells me that Bruce Ratner may randomly show up on an MSG broadcast again at some point or that the team will schedule one of next year's pre-season games at the Barclays. It wouldn't be quite the same if rescheduled, as a lot of the initial momentum is now lost. While Islander fans are certainly divided on the issue of Brooklyn, there was a large segment that seemed to be generally excited about it. On top of that, it was an interesting idea (and negotiating tactic) that will lose some of its luster the next time around.
There's still more to this story, even if the Islanders don't end up going to Brooklyn in 2015. But it's a shame we aren't going to be able to see it happen here and now.