We all know that Darth Maul was chopped in half by Obi-Wan Kenobi at the end of episode 1. But does that really mean he's dead and couldn't possibly be in the next one. I think that he could be back (and hope that he will be). Just look at Darth Vader. He was pushed into a lava pit by Obi-Wan, but still lived with a respirator. Its possible that something of the same sort may have happened to Maul. Maybe Darth Sidious sensed his apprentice getting sliced in half, and ordered some of his lackys to retrieve him. Than later they nailed him back together (or something of that sort). Or maybe the Darth Maul in episode 2 is just a clone of the first one, or the clone is the one who died. Anything could happen. A rumour that I've heard is that Ray Park (aka Darth Maul) has signed on to be in episode 2 (but we know how rumours can be, especialy when they concern Star Wars).
Also, Darth Maul is Zabrak, this species come from a planet that has very harsh conditions, so naturally Zabrak have great discipline, which would alow them to tolerate tremendous physical suffering. Darth Maul could have crawled his way back to his ship and flown away. This is possible because all he lost was from the waist down. This combined with his jedi skills, he may have survived.
This is just my opinion. We will all have to wait and see.