If You Didn't See Them Die, They're Not Dead

Death is a horrid and gruesome thing. Those who have seen it should not want to see more of it. Death is often a taboo subject, at least to some degree. We try not to dwell on it much. That is why it has been quite common not to actually depict death in stories. Always, there are euphemisms or it happens off-screen.

Nowadays, you can't use implied death; too many storytellers have tricked their audiences. This is exceptionally bad in comic books, where superheroes die surprisingly often, but none of them actually stay dead. They are always resurrected or rebooted. You also have the problem with too many spy stories where a character ultimately fakes their death to be able to move around without being suspected. 

Because this technique is so common, it is now cheap. It also breeds a certain mistrust amongst readers. If you haven't seen a character actually die, then they aren't actually dead. It may not be the funnest mindset to have, but it will prevent you from being played by an amateur author with cheap tricks.