Ha, ha . . . funny one, Mrs. peacock

Of course, we know the real reason was that Sean Connery opted not to appear in Indy 4, so the writers decided to kill him off; although for the sake of continuity with the Last Crusade storyline, it might've been better to just have Indy say that his Dad was still alive, that he was off aging gracefully in retirement somewhere, and that he just didn't want to go on another journey (basically Connery's real reason for not wanting to be in the movie).

But a point of clarification is in order here: my understanding of Grail lore-- as it was described in The Last Crusade --is that drinking from the Grail makes you live longer, but not forever. Remember, in the story that Indy was discussing with Walter Donovan earlier in the film, one of the knights of the Crusades told of the Grail's location before he died of "extreme old age" (and presumably, the knight drank from the Grail).

Presumably Indy himself will live for a very long time; but eventually, he will die.

My thoughts are when they were in the temple the knight said yes if you drink from the cup you can live forever but only in the confines of that room. Once you crossed the threshold to the outside world, then the elixir would not work.

I always thought AusFem's explanation is right, but BOTH of your explanations work perfectly! :)

I always thought Donovan should have had Indy or Elsa drink from the fake Grail before he drank from it, in case it wasn't the right one.

A friend of mine, while we were watching this scene, leaned over and said to me, "I bet Indy could've drank from any of those chalices, and he would've been fine." In that view, the test is one of worthiness, not whether or not one chooses the correct physical Grail. It also points to the view that the Grail-- contrary to Donovan's belief --is not some random magical talisman, able to give power to whoever drinks from it, but rather, is a holy artifact that will only reward the just.

@ausfem said:

My thoughts are when they were in the temple the knight said yes if you drink from the cup you can live forever but only in the confines of that room. Once you crossed the threshold to the outside world, then the elixir would not work.

That was exactly it, yeah.