In the final scenes of Edge of Tomorrow, William Cage drops grenades onto the Omega which then blows up and this ends the war with the Mimics. Before he dies, William comes into contact with the Omega's blood and rewinds time to the moment before arrival in London.
Since the Omega is now dead, does it mean that William retains the ability to rewind time and therefore becomes essentially immortal?
That depends on how the in-universe logic works. For example, from the Wikipedia description of the plot, it would appear that the death of the Omega mind knocked him back to the beginning of the loop to the point that the paradoxes would not happen. That is before the entire series of resets and loops. Additionally, since the Omega no longer exists, it cannot affect anything including those who would have the blood of the Alpha or Omega. From the way it sounds, his next death would not affect anything. Of course, the fact that they plan a sequel may mean that they will change the rules.
As for whether or not Cage is still able to time loop with no Mimics left on Earth, the post-Omega reset should be Cage’s last. It can be assumed that without the Mimic collective around, Cage no longer has the power to reset time. Still, he might want to ask for a blood transfusion, just to be safe. Otherwise, Major Cage is now free to debrief Vrataski on what actually happened – over a cup of coffee (with three sugars).
In the original story All You Need Is Kill the hero must kill the heroine so that the nexus ((called the Omega in the movie) will be unable to reset time. This is done by handwaving.
