I think that Denethor's death was inevitable, but I don't think that he necessarily deserved it. Of all the characters in the story, I think Denethor suffered the most in the film treatment - not through John Noble's performance which was excellent - but through the screenwriting.

In the film, Denethor is seen as already going mad, uncaring, stubborn and ineffectual yet this is not how he is portrayed in the books. Very little of what you see in the film can relate back to the book version so it inevitable that he has become such an evil figure.

The book Denethor has the beacons lit before Gandalf even gets to Minas Tirith and is in complete, and sane, command of the forces of Gondor up until Faramir is brought back injured. The relationship between Denethor and Faramir is a lot less hostile as well - when Faramir is sent back out to fight, the battle is still going on so Denethor is not sending him out to die.

The only reason that Denethor has to be killed off is that he is not willing to stand down for Aragorn. Not surprising as he has been ruler for thirty odd years - and his replacement is Thorongil, who was more important to Denethor's father than Denethor was. It's simply too sticky an issue for them to work around, so it is better if he is just removed from the picture.

So in my opinion yes, he had to die, but he did not deserve it.

Many that live deserve death. Some that die deserve life. Can you give it to them? Do not be too eager to deal out death in judgment. Even the very wise cannot see all ends.

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...so yes Denethor deserved to die, plus he treated Faramir his only living son like dirt. GRRRRRRRRRRRRR.......I hate Denethor so much!!!!!!!!!!!!