The most common and most likely answer to this crossword clue is the 7 letter word TESTATE
I've seen this crossword clue in The Sunday Telegraph
T
E
S
T
A
T
E
More clues leading to the result TESTATE
- I have will to rank without love
- Where there’s a will, there’s a —
- Willing to investigate cause of mischief?
- Leaving will prove a trifle gutless
- Pilot put away food with a will
- Having a will with notes on gallery
- Having the will to help others following on?
- Willing to cut landed property
- Willing to examine mischievous goddess
- Willing to examine a note
Buddy explains!

The straight part
We know that "Finally left everything one owns, being this" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case finally left everything one owns, being this = testate.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 TESTATE mean?
TESTATE noun- One who has left a valid will and testament
- Having left a legally valid last will and testament (of one who has died).
- Having a test (external calciferous shell or endoskeleton)