Boyle on Ending
Danny Boyle was present for a Conversation after a showing of Shallow Grave at the Academy Theater in NYC this week and he definitely said (in response to a private question after the talk) that Alex is still alive. He had remarked during the conversation that screenwriter/physician John Hodge had stressed how callous and seemingly cold medical personnel can be. We see that in the last scene when they're photographing Alex while he lies there, waiting for the knife to be safely removed.
Fact is, Alex didn't kill anybody and was defending Juliet when he was stabbed. He is a jerk but he's retained his humanity more than the other two.