Earlier quoted context omitted.
Why destroy NS1 then and not NS2 (NS1 and NS2 both have two pipes and only one of the two NS2 pipes were destroyed)? And why destroy it at this exact time when Russia was already coming up with less and less plausible excuses to halt deliveries via NS1 (both NS1 pipes were destroyed)? Why not wait with the nuclear option until there were even signs that NS2 would come online (Germany had already halted the certificat…
The article implicitly suggests that the goal was indeed to sabotage both pipelines fully. It doesn't say it outright, but if the hastily re-programmed explosives were triggered by a sonar buoy after three months in sea water as the article says, then it would not be surprising at all if some of them failed to go off. Precisely that the article implicitly gives very plausible answers to good questions like yours, is…
In addition the bad-trigger scenario would imply that the explosives and triggering mechanism remained in place on the remaining pipe, which would require the US to rush there to remove them or trigger the missing one to avoid terrible diplomatic consequences if the unexploded device were to be discovered.