Would it melt before then? Interstellar space is extremely thin, on the order of 1 atom per cubic centimeter (estimates vary). But, as we learned when Voyager finally left the solar system a few years ago, it is hot as hell. More than 54,000 degrees F according to National Geographic:
The Voyagers didn't have today's ion engines. I don't know how much that gains us, though, as the main speed gain was by leeching momentum from planets' momenta, rather than from the hydrazine thrusters it carries
Orion drives can get up to some respectable fraction of the speed of light. Just need a billion or so 1-kiloton nukes. No biggy. No worries about sneaking up on them and startling them either.