Situational play:

League has a "no play at the plate" bylaw.
The runner merely must cross the scoring line before the catcher gets the ball and touches home.
There is no commit line between 3rd and home.
The runner is nearly home (over 2/3's of the way), sees the catcher will make the catch and retreats to 3rd. Safe or out? Merely wanted some input as to how an umpire would handle this...

Without a commitment line, safe unless put out prior to reaching 3B.