It keeps going until we lose communications with it. That's what probes do, they don't come back. Hell, I'm pretty sure we're still getting data from Voyager.
until we lose communications with it = Until aliens take it and turn off it's transmitter then use it to find earth and come take all our mineralsOR until it gets hit by a meteor
What good minerals could they possibly want?
we have lifdoff
what, did you never watch star trek: the motion picture?the aliens modify it, it becomes self-aware, and it tries to kill everything.