The most common and most likely answer to this crossword clue is the 11 letter word STALACTITES
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More clues leading to the result STALACTITES
Buddy explains!

The straight part
We know that "They should hold on!" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case they should hold on! = stalactites.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does STALACTITES mean?
STALACTITES noun- A secondary mineral deposit of calcium carbonate or another mineral, in shapes similar to icicles, that hangs from the roof of a cave.