The current MacHeist bundle is a "Best of" collection from the previous two bundles. Per the MH directorate in their online forums, this retail bundle will be available for about a year online and, potentially, in some retail stores. Some of the apps may be changed during the year, but by and large you will have plenty of time to buy the bundle. I wouldn't recommend rushing into buying just yet. Get the Macbook first, play around with it and gauge your needs. From there make an educated decision as to whether the apps in the bundle will actually fit your needs and be useful to you. While you will not likely use all 12 apps regularly, if you are not getting at least some use out of 3-4 apps (minimum) then it likely wasn't worth the purchase price for you versus buying the apps directly from the developer.
The MH directorate has also referenced a MH III coming "later this year", presumably with a new bundle of apps No more specific timeframe was given. It wouldn't surprise me if it coincided with either back-to-school promos or the Christmas/holiday season. I would also guess that Macupdate will do another one later this year, too, but that is only a guess. hat would most likely be a November/December bundle, too.