They usually have a patch of some sort for this kind of thing down the road.
I see what the issue is, being a backer with the digital tier, I don't have a disc at all.
So the kickstarter FAQ says there will be no DRM, though this policy was update. The GOG version doesn't have DRM.
As for an answer, historically, Larian has always made it possible to install a DRM free version of the game from all existing media (disc/digital) that was sold. In this case, I'm guessing an installer program will eventually be released that when executed, will ask you to insert the disc and it will bypass all DRM requirements/prompts.
In wibbles defense:
Larian did fail to update their DRM policy on the kickstarter FAQ page.
In Larian's defense:
A lot happened since Kickstarter for them to decided on changing their DRM policy. Steam so far seems to be the most successful and least draconian of all DRM out there.
DRM free can still be purchased at
http://www.gog.com/game/divinity_original_sin or from the Larian Vault (can get access from Larian.com and its at the top).
With digital downloads so popular, I'm not sure if a DRM free DVD will be released. An update to allow a DVD installation to bypass DRM would be more feasible. But this is me going off historical data, not the current business policy. I'm guessing the install would go like this.
1.) Download DRM-free installer for D:OS and run it. (when/if it is released)
2.) Installer will ask you to insert DVD.
3.) Installer will begin installing the game and bypass all DRM/Steam prompts.
4.) Game is now installed DRM free

Since all the previous games (not sure on Dragon Commander) are now DRM free, I'm expecting D:)S to become DRM free at some point. Swen has stated in his blog that for him to play games when he was really young, he got pirated versions. I don't remember if they were free or much cheaper, but he's not a big fan of DRM. Though he's also got a family to feed along with the other developers.
As Larian Studios is a business, we'll find out when the DRM update is released (if it will be) when they release it. We'll most likely have no advanced warning of this release. It will probably come out as an expected game update and that is when we will see in the notes that the update will strip all the DRM.