The most common and most likely answer to this crossword clue is the 5 letter word SWANS
I've seen this crossword clue in Independent
S
W
A
N
S
More clues leading to the result SWANS
Buddy explains!

The straight part
We know that "partners for life?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case partners for life? = swans.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 SWANS mean?
SWANS noun- Any of various species of large, long-necked waterfowl, of genus Cygnus (bird family: Anatidae), most of which have white plumage.
- One whose grace etc. suggests a swan.
- This bird used as a heraldic charge, sometimes with a crown around its neck (e. g. the arms of Buckinghamshire).
- To travel or move about in an aimless, idle, or pretentiously casual way.
- To declare (chiefly in first-person present constructions).