Just as with Iron Man 2, Rourke was approached about the role but it all fell apart when it came to cutting the deal. But it would seem Lionsgate really wanted Rourke, and his interest in the Hyborian Age had been whetted just enough, because they returned to the table and made friends. They then drank some ale, swore blood oaths, and brought in the slave girls. It's the Hyborian Age, after all!
In all seriousness, I think it's a good sign for the film that they continued to seek out Rourke. The story has Conan embarking on a quest to avenge the slaughter of his people. One of the dead includes his father, Corin, so it's likely to be a flashback heavy role. (I guess Mom doesn't get any flashbacks. Probably died in childbirth. A better fate than death at the hands of enemy swords, I suppose.) The fact that they want Rourke instead of just any actor who can be old and stoic says quite a bit, and I certainly hope it's a sign of good casting to follow. Conan is set to begin filming in Bulgaria this March.