Note: I know this cliché was talked about quite nicely in the last volume of this series, but now that I am a bit older and wiser, I want to expand on it further.
No matter what perspective a book is set in, the main character remains one of the chief cornerstones that helps a story fully develop. They are your shoes to walk into the fictional works you are to experience for yourself. Everything they see, they hear, they feel, you experience firsthand. We cry at their struggles and connect with them when making a life changing choice. Without the main character, the book cannot function.
That is why killing the main character is a risky move that way too many writers have taken the liberty of using to "tie up all loose ends". When the main character dies, so does the heart that makes the story function to its fullest capacity. Unless the cast has multiple main characters or this character is resurrected in a fashionable way, the plot built up for so many pages is dead. We lose our eyes to the story.
Imagine what would have happened if JK Rowling, the author of the Harry Potter series, decided to kill off the titular character she had built up for seven books. Not only would it had upset longtime fans who waited for years to read the last installment, The Deathly Hallows, but the series as a whole would have been tainted forever. She actually almost did such a move, but after a chat with horror novelist Stephen King, she decided to keep the character alive and give the fans an awesome finale. Without knowledge of the damaging effects killing the main character has on fantasy book after fantasy book, JK Rowling would have messed up big time.
The same applies to every writer from every famous fantasy series out there. Without the main character, what do you have? So if you ever find yourself thinking for one second to use this cliché when writing a fantasy novel of your own, ditch it immediately. Your fans and critics, as well as the story itself, will thank you for it.