After lurking on this forum for the past month and reading all the heat, I have to say this is the poster child for open source. Doing so would actually increase the quality of the product and probably increase the rights the author has. By encouraging forks, and forcing the derivative works to contribute back, the author would gain that work.
Right now there's really nothing the author could do if someone wanted to fork carbonite, as the copyright is on the non derived art assets(if there are any), and the code itself. Blizzard, by the EULA, asserts its own copyright on WoW which covers how the UI is layed out, and that fact is the main reason why add ons cannot charge, well in a legal sense.
Making a project OSS doesn't stop you from asking for donations, many many OSS projects ask and get donations.
It would definitely have helped this situation, and the end result would have been the same.