From Matt Bishop at MMA for Real whose interview with Kevin Iole broke the story:

Iole said said Affliction had approached the UFC about merging the week before UFC 100.

This came after Iole reported a potential merger of sorts between Affliction and Strikeforce, which was brewing early in the week, even prior to Barnett's drug test failure, Iole said.

"Somehow that fell apart," Iole said. "I think it was because Scott Coker, the CEO of Strikeforce, was out of the country and the paperwork wasn't signed," Iole said.

"Right now, I'm not exactly sure how that fell apart, but at the last minute it crumbled, so it opened the door for the UFC."

Iole adds more at his own column:

Later in the day, Affliction came to terms on a deal in which it would quit promoting fight cards. However, the status of the fighter contracts belonging to Affliction is unknown.

They could revert to the UFC or they could become free agents, able to sign with the promoter of their choice.

I said it before and I'll say it again: Scott Coker picked the wrong week to go on vacation.