At the end of The Last Crusade, the Austrian woman attempted to take the Holy Grail beyond the great seal at the entrance of the temple.
In doing so, she caused the temple to quake and the Grail fell into a chasm that was created.
One of the last scenes in the temple shows the last Templar Knight waving bye to Indiana as the escaped.
Was the grail completely lost to the world now? Or did the Knight collect it and reset the temple for the next person to face the tests and discover the grail?
Yes
These people at this reference, interpret the final grail scene the same way I do:
The Grail is lost forever. (bold mine)
Elsa grabs it and runs off, but when she crosses a forbidden area, the temple collapses, and Elsa and the Grail are lost forever.
The Wikia site for Indiania Jones says this about the Holy Grail(bold mine):
Indiana nearly tumbled into the abyss himself, but was caught by his father. Indiana, like Elsa, tried to reach the cup, but was persuaded by Henry to let it go.
As a result, the Grail was ultimately lost following the events of the adventure, but the experience gave both Indiana and his father the chance to rekindle their rocky relationship.
Also that page mentions:
Years later, the elder Jones remarked on the elusive, indefinite nature of the Grail, commenting that the cup discovered by the father-son team was simply "a Grail. But many of the oldest Grail texts, written by the most ancient seers, refer to the Grail as an elixir, as a bread, a powder, gold, or a stone."
This part of the story was intended to be left as a mystery by the writer, and so the public would have to imagine (individually) what happened to the Grail.
Another point in favor of 'yes': The Grail is seen (and noted in the script) to be a clay cup with gold foil lining the bowl.
When it fell into the chasm, it undoubtedly shattered into a whole lot of shards and dust, so it isn't even a cup anymore.
