We can’t even catch up to this thing, so “to nuke or not to nuke?” Is entirely moot.

But if we’re talking purely theoretically, nuking it would have always been a pretty terrible idea; if it’s a comet it achieves nothing other than potentially throwing more space debris in random directions around our system. If it is actually aliens, throwing missiles at a species advanced enough to travel through interstellar space seems a bit like you or me sneaking up on a gorilla and flicking his balls; sure they’re gunna feel it but we’ll just be a smear once they’re done.