Andy The only problem with the ending was he killed Deb, if he had gone into the storm and ended up lost that would have been ok because he would of had a way back in with some kind of amnesia.
Everybody was being written out - it was the finale; the end; finito.
That being said, now that it is no longer "the end" of Dexter the death of Debra need not hinder further screen time for her; it had little effect on Harry.
Jennifer Carpenter has spoken about the (first) finale for Dexter.