A maul has formed, you call maul. The team not in possession clearly want to hold the ball up, but the team in possession get the ball clearly to ground. Under law 16.16.b, the maul is over. How do you now proceed?
Play on. As the ball is now clearly on the ground, then it is either available (as required by Law 16.8) for the scrum half (or another player of the side who had the ball when the maul formed) to pick up and play (that is if it’s at the back of what was the maul) or available for the players remaining on their feet to contest as a ruck (that is if it’s still within the confines of the players on their feet) in what was the maul.
Effectively this creates a situation similar to a post tackle ruck – i.e. ball on the ground being contested by players on their feet.
A ruck cannot be changed into a maul as no player in a ruck is allowed to handle the ball, but there is nothing in law which states that what was a maul cannot change to a ruck. Indeed imagine a post lineout maul where the catcher then drops the ball (straight down or backwards) and all players remain on their feet pushing against their opponents – this is obviously now a ruck – and no offence has been committed.
If the ball carrier goes to ground without getting the ball to ground, opponents do not have to move to allow him/her to do so. This would be an unsuccessful end to the maul (ball unplayable).
Principles of the game:
The laws are written to permit continuity of competition for the ball. We should only stop that contest if an offence has been committed (and no advantage gained by the non-offending side) or the ball has become unplayable.