Lost in Space

I recently learne that NASA is planning to send a probe to Europa in 2015.
But for some reason, I started thinking, what if it was not an unmmaned
probe that we were sending, but a manned mission to Europa.
Let's just say.
Not an easy mission. A dangerous misison even. It would take six years
to reach Europa. That's along time. Its a long, long way to go.
780,000,000 km from the Earth. Long, long way. And becuase of the way
my brain works, I suddenly wondered what would happen if, for some
reason (never mind how) it went dark. All communication was lost with
the vessel.
I wondered a few questions. (please don't sniker if they sound stupid)
One, would we still be able to track it? Or would it be "lost". Could
telescopes see something that far that is so small? (a research vessel
would be quite small compared to planets or moons) Basically, could we
"lose" it?
Two, if it was possible to "lose" it once we lost contact, would we,
NASA or ESA for example, bother trying to mount a rescue mission? I
would imagine building another vehicle capable o just a journey...would
be expensive. Would we spend millions to resuce five or six people.

Just wondering.
Dean