Some items, such as the book, will be available after the Kickstarter campaign has concluded. However, you obviously will not be recognized as a backer in the book.
The artwork print from Joe Simko will NOT be printed after the campaign has ended! That means this is your only opportunity to get a copy of this amazing piece of art.
The game will likely be available after the campaign, however it will be at a much later date, and will likely not include a lot of the extra items such as a box, manual, or other special items. The Joe Simko artwork is also exclusive to the Limited Edition which will only be available during the Kickstarter campaign. There also may be subtle changes to the game content for the retail release of Black Box Challenge.
Other add-on items, such as the Perler bookmarks or the original book, will also be available after the campaign has ended.