I had a look at the Rotax web site, which specifies an idle speed of 1400 RPM on the 912. There is also an SB that says you must not idle below 1200 due to the risk of damage. I tried the experiment today in a 15kt headwind. I touched down at normal speed where the numbers would be if we had any. The runway has a slight up slope and I did not touch the brakes at all. I used up most of the 450 metre runway despite the up slope. I then repeated the exercise landing at the same speed but cutting the mags on touch down. I rolled to a halt in less than 200 metres.
I expected a reduction but was surprised how much it was. The stationary idle prior to takeoff was 1800 RPM and with power off prior to landing about 2000 RPM presumably due to windmill effect. It was also interesting how long the prop took to stop when I cut the mags due to the same effect.
This is a useful exercise to try for yourself so you get a feel for how short you can land if you really have to.