The most common and most likely answer to this crossword clue is the 7 letter word WIDOWED
I've seen this crossword clue in The Times
W
I
D
O
W
E
D
Buddy explains!

The straight part
We know that "left alone" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case left alone = widowed.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 WIDOWED mean?
WIDOWED verb- To make a widow or widower of someone; to cause the death of the spouse of.
- To strip of anything valued.
- To endow with a widow's right.
- To be widow to.
- (of a previously married person) Whose spouse has died or is gone missing; who has become a widow or widower.