VOYAGER - how far can it go?

Not much longer, it's radio-isotope thermoelectric generators are almost cold now. Both voyagers will cease any science operations finally in approximately 2025, when nothing bad happens.

Most power hungry instruments are already disabled anyway as the power generators gone too weak already.

The RTGs generate always power by decay of plutonium, regardless how much power is needed. As the decay rates drop by 0.787% per year, so does the power output.

The Voyagers (1 and 2) are pretty much at the edge of the solar system, defined as the region where the solar wind slows and is stopped by the interstellar wind. It is estimated that they have enough power generation to last about another 20 years. After that, the power from the radioactive decay will not be sufficient to power any of the onboard instrumentation, and the Voyagers will go dead, continuing outward through interstellar space to whatever fate awaits them.

To some extent, the amount of time that Voyager can send us information is dependent on how big our radio dishes can get, and how sensitive they can be. They are already considerably better than the receivers available when Voyager launched. If we still had host receivers, the mission would already be over. Current estimates (1998) are that increasingly limited instrument operations can be carried out at least until 2020.

The craft will continue moving, however, into interstellar space.

It can GO forever or until it hits something big enough to destroy it.

Around 2025, possibly later, the spacecraft will no longer have enough power left to power any of its instruments. Several instruments will run out of power before then, and the solar wind detector stopped functioning in 1990.

Generally it can go as far as it likes and will never stop unless it hits something or vice versa, it will just be so far out that we will not be able to control or make contact with it. It will just drift endlessley through space, bearing in mind nothing ever wears or decays in space, it just stays in mint condition unless it was hit by a meteor shower or something else along those lines.

with a little luck, until it makes it to the edge of the Solar System, which it should do in another 20 years or so.