It may have exploded already, because it is 400-600 light years away what we see is it 400-600 years ago. If we are viewing it through a telescope we'd see it a little closer to as it is now. The Gamma rays wouldn't reach earth until we can see the explosion, preferably unaided.
I highly doubt it could be dangerous, first of all the beams have been travelling for 400-600 years and spread out, what does hit us probably will be a minuscule compared to what the sun hits us with everyday.
Native: English (NW American)
Beginning: Arabic (MSA/Egyptian)
Some day: German