But he would leave Casey if he thought it would make Casey happy. I think it's pretty obvious Dan would do anything, up to and including assisting in his pursuit of the craziest woman ever Dana.

So what if, instead of instituting the super-crazy 6-month dating rule, Dana just dates Casey in the beginning of season 2? After what happened with Casey's ex-wife, Danny is aware that Casey is more than willing to sabotage his romantic relationships in order to maintain his relationship with Danny. If he thought Casey was going to do that again, I can see him trying to remove himself from the equation. The station is in trouble at that point and Danny's in the middle of a pretty serious bout with depression, so I can see him just deciding to get the hell out and move as far away as he can...

Hmmm....