Next flight
The next Shuttle flight will service the HST and the astronauts will install the Advanced Camera Surveys.
Apparently, it will be 10 times more efficient than the FOC.
The ACS will be put in FOC's place, which means that the COSTAR won't be needed either, I believe. Every instrument will have built inside it the corrective mirrors needed to compensate for the main mirror's sphericity aberration.
Raoul