I assume the Russians have some sort of valve on their end of the pipe that they could switch off. That would be cheaper than blowing the pipe up, and also givem more negotiating leverage.
Yep, and putin has said that he'll close the valve (well, not him personally).
EU gets cold, and the only way to heat up is to sit down with putin and make some sort of an agreement.
Now, someone destroyed the pipeline, and there's no incentive for EU and putin to make any negotiations, since the pipeline won't be fixed before the winter is over.
It probably wasn't them.