The most common and most likely answer to this crossword clue is the 9 letter word TOMORROWS
I've seen this crossword clue in Financial Times
T
O
M
O
R
R
O
W
S
Buddy explains!

The straight part
We know that "days to come" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case days to come = tomorrows.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 TOMORROWS mean?
TOMORROWS noun- The day after the present day.