Okay, with the cancelation of SM-4 how long does hubble have left?

The articles I've read list 2007 as the time period when it will likely become
useless as a scientific insturment. But when will it likely come crashing back
to Earth? And how long can Hubble go without servicing? Let's say by 2007 the
gyros fail and Hubble can't be pointed anywhere. Are there any other critical
systems that would likely fail without the Shuttle to service HST?

Basically, at this point I see SM 4 as dead with Bush in office and his fantasy
space initiative becoming NASA's priority. If enough pressure is put on NASA
can an HST repair mission be launched between the time Hubble becomes a dead
bird and it re-enters earth's atmosphere that could bring it up to operational
capability?

I'm hoping if Dubbya fails re-election and the following administration doesn't
share Bush's ideas for space NASA might become more inclined to put SM 4 back
on the books...

-A.L.