The most common and most likely answer to this crossword clue is the 3 plus 2 plus 5 letter word LIE IN STATE
I've seen this crossword clue in The Daily Telegraph
L
I
E
I
N
S
T
A
T
E
More clues leading to the result LIE IN STATE
Buddy explains!
The straight part
We know that "What monarchs may do ultimately" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case what monarchs may do ultimately = lie in state.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.