Complex sentence: Sam, realizing that Liz might be happier with Nick offers to sacrifice himself and attack the bear so the other two can escape, as he is dying, Nick rushes to help and is killed as well.
Split into simpler sentences: Sam, realizing that Liz might be happier with Nick, offers to sacrifice himself and attack the bear so the other two can escape. As he is dying, Nick rushes to help and is killed as well.