The perfect solution I think it would be an extended season, or maybe season 9 to be aired in January - February.
The question shouldn't have been "will it" but "should it". I think 8 will be the last season but I for one wouldn't mind it going into a 9th.
This isn't about whether showtime wants to pull the plug. Despite loving the characters and the show and being eternally thankful for the opportunities it has brought them, I think the cast, most especially Michael C. Hall and Jennifer Carpenter are ready to move on in some ways.
There are other characters to explore out there, other projects such as stage and movies. They have probably passed on many great movies over the last 7+ years and it would be unfair to force them to stay on a show that until this season had been lagging.
This season has made us forget how much an endgame and end date was needed. Once that happened, the writers knew they had the material needed to make Dexter better in it's final stretch run.
Dexter may be that rare phenomenon in which it's ratings have gone up each season long after most shows ratings fall after say the fourth season or so.
I for one think it's great they are ending it. Give it the excellence it deserves in it's final two seasons and be thankful it made it this far.
It would be odd indeed for the plug to be pulled on a show that people eagerly watch..wierder decisions have been made by those in charge...perhaps a word from the dexterites would help?