I get that the boys are in a state of war against "evil" while at the same time they are attempting of saving Dean from going to hell. Since Dean situation seems to be more and more grim with dear ole Bella stealing the cult (that probably could have been used to kill the demon contractor or at least used as a leverage, etc) and Ruby admitting to Dean she can't really save him etc. Dean might have to die & become a demon himself (I shiver at the thought of it! but it looks like it might happen much to my dismay)... Anyways someone had a thread of what Dean might do on his last day, we have already seen what he has been doing over the past "year"... enjoying life as much as possible by doing all these crazy things as well as calling up a couple of his old flames, etc However, since his run in with Lisa and realizing some of the things he never got to experience and would now be missing out on... I think it would only be natural for him to go back to the one he loved?
Like a soldier going to fight in a war where he might be killed or like someone whose dying of an illness shouldn't he be saying farewell to his one true love or at least try to see her one last time? Now I know all of the haters going to jump on me for daring to suggest that the writers should bring back Cassie and provide some form of closure to her character once and for all. Especially, since things were left on Dean's note: ''I'll see you again Cassie, I will'' to me it felt like he really meant it and I would hate to believe that Dean is not a man of his words
Some may disagree and say that he is over her, I beg to differ I think the only reason we never heard Dean mention her ever since has to do with the fact that she was his weak spot (with exception to Dean's fear of flying and his family). One could tell from when they sadly departed how deeply Dean was affected by it that he wasn't willing to even address it. As we are all aware of, Dean doesn't allow himself to show such tender and affectionate emotions that easily. Hence I think she is still stashed somewhere in the back of his mind (especially with him now possibly "dying"). It would only be logical, in my opinion to have him say his good bye to the one lady in his life that wasn't a mere one night stand. This is why it would be interesting to bring Cassie back in season 3, like they have done with the other of the characters.
Now the question isn't whether you liked Cassie or not, but story wise is it not only reasonable that Dean would think of reaching out to her either in/directly in his coming final days?