Thanks to a slightly related comment elsewhere I was recently reminded of the third (and final) Indiana Jones movie. At the end of the movie it turns out that while the Grail does grant eternal life, any attempt at removing it from the temple causes
the latter to collapse.
Assuming that mechanism makes it absolutely certain the Grail's cup cannot be removed from the temple (and even if it could, the other half, the "water" which certainly wasn't pure water, was still inside the temple), were Indiana Jones' actions mostly in vain (aside from saving his father)? It seems all the Nazis could have achieved was
living forever inside the temple
which was not exactly useful...