Reality is this set could last anywhere from a few months to 5 years. It's also likely that if you don't get this initially, you might not be able to get it until weeks or months later. A similar situation happened with other similar sets, like the recent Batman Tumbler. Lego has a track record of undershooting demand for these kinds of big one-shots, then catching up later. I doubt you'll not be able to pick one up eventually, as it's not a limited edition or anything.
Being an exclusive, it won't be available in normal retailers (
Amazon, Target, etc.) for a while, if at all, but you will be able to get it from Lego directly and apparently Disney Stores too.
This will be officially available September 1st, but likely this will be available early (middle August) for Lego VIP members (anyone can join).
From my view, if you want it, get it whenever you can. This thing will be ridiculous on the aftermarket.