I've heard that the limiting factors wrt Hubble's current life span are
the batteries or the gyros. The batteries being an obvious one, while the
gyros may not be. If they are just being used for attitude determination
during maneuvers, and not the actual maneuver, it should be possible to
extend it's life so that the batteries or orbital decay are the limiting
factors.
HST doesn't "maneuver" at all. It used to rely on occasional visits
from servicing crews for periodic reboost.

Tsk, tsk, Herb - "manoeuver" includes changing the pointing to look at
something interesting.

AIUI, the gyros were expected to last longer, but they have some sort
of design/manufacturing problem that makes them die much earlier than
expected. They are not only required as sensors for pointing - fine
guidance is done seperately by the fine guidance sensors - but to
stabilize the whole craft against torques. Not enough gyros, not enough
stability against random torques.

Jan