I been thinking about this very thing. The chainring really doesn't protrude from the BB/motor housing so it kinda seems unnecessary, but there is a third bolt hole there to allow for a full guide/guard to be installed. Found a nice deal on an mrp amg v2 that will cover up to a 34t sprocket...
I lost mine the first ride too. I used some mastic tape for a temporary solution. I then ordered some small sheets of kydex (gun holster material). I used the paper backing from the original as a template, and cut a piece to fit, formed it with a heat gun and attached it with some 3m automotive...