
I hate to belabor the obvious once again, but if there had been an Orbiter
emergency in the early stages of the original HST deployment mission, they
would have HAD to land with HST in the bay. 

Indeed they were worried about that.  One concern was the possibility that
they would lose a motor or something on the way up, and make orbit but one
that was too low to give HST a useful lifetime against atmospheric drag.  
I believe the decision was to deploy HST even if the projected lifetime was
as short as six months.  In fact we got an excellent orbit, on the upper
envelope of what the Shuttle can do.

I have never heard of any serious consideration that HST might be brought 
down for refurbishment.  You would have the horrendous cost of transporting,
cleaning, re-testing, and re-certifying all the hardware on the ground, in
addition to the lost observing time and the cost of a second deployment 
mission with the risks that we might not get such a good orbit the second 
time.  And, you would probably STILL need a (third) servicing mission in a 
few years as gyros and other components wear out.  Better to have two 
servicing missions in space (which could well happen) than to bring HST down 
and take it up again.