Nah Dexter loves Deb way too much to kill her ...he is more of a protective brother despite being well the serial killer ...but I can't say the same for deb ...I have this notion that she might just shoot him ...and even then dexter won't hurt her ...not that he understands emotions much ...but to him deb is the most important person in his life along with his son now ...
The very first epi of dexter was where dexter was introducing his life and people around him and there was this beautiful thing he said about deb ...that she is his sister and if he could actually feel love ever he would have loved deb ..and that explains all ...if he can be human ...he will surely be that for her ...and again he is that guy who killed his own blood brother to protect his foster sister...I hope it stays the same ...rather I think dexter might just turn himself in if deb asks him too ...