Yep, wishful (but sensible) thinking to imagine you could spot a 'bumped' a/c before you went flying in it.
The rate of crack propagation that would ensue following a bump means that the mast would separate in seconds. Unfortunately, unlike a blade being shed, you'd know all about it too!
There is a classic (true) tale of an instructor, in Iran at the Bell school, doing engine off landings. On one particular landing there is a strange noise on touchdown and after a moment they realise there are no blades. The mast had fractured at as they landed. If this seems to contradict the above, it was a quality problem in manufacturing and this was the first crew to live and tell the tale.
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Another day in paradise