no leave it there...
and the underbody plastic can stay, if it reaches the bumper, then it can be attached to it..
otherwise, I guess it would come off...some bumpers may not extend real far back.
VSGTS14, now that i think about it, i would also reccommend leaving it if you can. But it all really depends where you live. Out here is California, it i don't think it would be of any problem.