That makes no sense for anyone but Russia (leave the option slightly ajar for selling gas later on). And the contracts would not quite be irrelevant since they could then try to seize more assets from Russia.
Also a Norway-Poland gas pipeline was opened up just one day before the NS attacks, so could also be sending a message.
Maybe they wanted to, but simply failed? One of the bombs did not go off, or something like that.
A former Navy SEAL was interviewed and stated pipelines are what they called (IIRC) "friendly targets" — it doesn't take much explosive to take them out (I imagine their pressurization helps, but I don't have subject matter knowledge).
Doubtful. I think the most rational reason Russia might have done it was to remove a bargaining chip from any Russian challengers to Putin. But this seems like a stretch; if Putin thought some gazprom executive was going to use the pipeline to negotiate a peace with Europe, he'd probably just order that executive and his family murdered. That seems to be the way he operates.
Self-sabotage to preempt coups is not unheard of though. The organizational dysfunction and poorly trained state of several militaries around the world is probably attributable in part to self-sabotage, by politicians who fear military coups.