Sure, it was incredibly obvious that season 7 would end this way. Lt Guerta finally succumbing to the collective bond exemplified by the Morgan siblings. But this is not what those last 3 or 4 dramatic minutes were about.
It was all about emotion and a love (albeit a strange variation of it) that runs deep. Peel the hard expletive laden outer shell from Deb and what you see is the frightened girl that can't bare to live life without her adopted brother. Jennifer Carpenter deserves an Emmy for those last few minutes alone as she showed beyond a shadow of a doubt where Deb's loyalty lies. However this loyalty has come at the ultimate cost, her innocence and ultimately her soul are now destroyed.
Dexter's realisation that this is the case only further solidifies in my mind that he has grown in empathy even if it is only confined to those close to him. Comparing him to Dexter in those season 1 flashbacks bares testament to this.
The fact that this season of Dexter has devoted it's time to fleshing out the relationship between Deb and Dexter only tells me that season 8 will likely be spent deconstructing it again. Deb has crossed a line (thereby ironically keeping Dexter's code in tact - just about). This will likely form the basis for season 8 and I look forward to the story that will be told. I somehow don't think its going to have a happy ending....