^^That's called a bump stop, but it does very little. Don't worry about its condition, unless you're planning on doing a couple of 3ft drops with your car
It takes a hell of a lotta force to bottom out your struts (they're struts in the front, not shocks). It can't be replaced anyway, unless you remove the whole strut assembly and take it apart.
The sleeve however, should be attached to the bump stop; it just snaps on to the bump stop. Together, they form a cover over the seal at the top of the strut housing, where the rod slides in and out. It keeps debris from damaging the seal.