If it is 650 light-years away and it exploded 640 years ago, we're in trouble. There seems to be a lot of uncertainty about its distance--I have an old World Almanac which says 520 light-years (so we are seeing the light that left there in 1492) but there are lower and higher guesses.
It's supposed to explode within the next million years. So I won't put it high on my things to worry about. As Louis XV would have said, Apres moi, le poulet frit.