The most common and most likely answer to this crossword clue is the 6 letter word PAGANS
I've seen this crossword clue in The Daily Telegraph
P
A
G
A
N
S
More clues leading to the result PAGANS
Buddy explains!

The straight part
We know that "heathens" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case heathens = pagans.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 PAGANS mean?
PAGANS noun- A person not adhering to a main world religion; a follower of a pantheistic or nature-worshipping religion.
- (by extension) An uncivilized or unsocialized person.
- (by extension) An unruly, badly educated child.