Jim, per Decision 14/3 for the 2018 rules...
14/3 Clubhead Separates from Shaft on Downswing
Q. A player starts his downswing and the clubhead separates from the shaft. The player continues his swing but no contact is made with the ball. Did the player make a stroke?
A.Yes.
As far as 2019 is concerned if you refer to the interpretation of a STROKE you will also find your answer...
1 – Determining If a Stroke Was Made
If a player starts the downswing with a club intending to strike the ball, his or her action counts as a stroke when:
The clubhead is deflected or stopped by an outside influence (such as the branch of a tree) whether or not the ball is struck.
The clubhead separates from the shaft during the downswing and the player continues the downswing with the shaft alone, whether or not the ball is struck with the shaft.
The clubhead separates from the shaft during the downswing and the player continues the downswing with the shaft alone, with the clubhead falling and striking the ball.
The player’s action does not count as a stroke in each of following situations:
During the downswing, a player’s clubhead separates from the shaft. The player stops the downswing short of the ball, but the clubhead falls and strikes and moves the ball.
During the backswing, a player’s clubhead separates from the shaft. The player completes the downswing with the shaft but does not strike the ball.
A ball is lodged in a tree branch beyond the reach of a club. If the player moves the ball by striking a lower part of the branch instead of the ball, Rule 9.4 (Ball Lifted or Moved by Player) applies.