I have never seen this particular crank, but judging from the pic, it won't pop off. even if it came loose, the hole in the center of the guard won't go over the bulged area of the crank arm (unless there is an opening behind the crank arm I can't see), so you wouldn't be able to slide it free. There may be a chance to remove it, but it looks like you would have to remove the crank arm first. Hard to tell from the pics!
My gut tells me your chain guard is integrated into the crank. It's a nice little annoying trick Shimano does on a lot of their parts. Break or wear out one part and you have to replace the whole thing.