I have seen Forbidden Planet so many times, I have lost count. What has troubled me for years is I know for sure I saw it at least once, if not twice where when the monster from the ID burns through the shields, it grabs Morbius and shakes, then drops him, thus killing him. You can clearly see the reaction from Alta and the Commander, but they never show it. WHY? I guess it was considered too brutal so they cut it. Does anyone but me remember seeing that in the film?
Here is a scan of an actual production script for The Forbidden Planet. There is no indication of such a scene, with the ending playing out essentially as in the final version of the film. Nor is there anything like this scene in the novelization of the film. So you must be misremembering.
Having the monster kill Morbius would probably not, in any case, make much sense in the context of the film. Since the id monster is made up of Morbius subconscious thoughts, it is acting according to his hidden desires—to keep himself and his daughter safe on the planet at any cost, certainly not to cause his own death. The climactic defeat of the monster comes when Morbius, finally understanding what is happening and making a literally superhuman effort, renounces and dispels the monster; and moreover, it only works when he really wants his daughter to go free and for the ship’s crewmen to come to no further harm. (See here: Causes of Morbius' death and the disappearance of the Id monster for Morbius’s death scene from the novelization, told from his own point of view.) A scene with Morbius being killed by the monster would ruin this.