The "Putin did it" hypothesis was that he did it to prevent internal replacement. Suppose that some Russian rival wanted to replace him. They could kill or imprison Putin, end the war in Ukraine, restart the gas pipelines, and have a lot of gas money from Europe to distribute to supporters.
Destroying the pipelines removed the potential reward for an internal rival to replace him.
Nah, that's too simple an explanation. Someone in China obviously wanted cheap gas, so they had to force the Russians to stop selling to Europe and turn eastward. But it can't be Xi because he was enforcing the lockdown, so must've been someone else. My money's on Jack Ma - rich, powerful, directly interested in getting the economy running at full speed again.
If Russia levels Kiev and starts moving in to the rest of the country, a) Ukraine will almost certainly not surrender, leading to prolonged insurgency, and b) I expect ground troops from neighbors, EU, and possibly NATO will come into play.
Meanwhile, all the rhetoric of Russia “saving” a brotherly nation goes flying out the window.
I'm afraid something as drastic as the annihilation of Kiev will lead to actions that are beyond the usual risk assessment levels. Countries will be compelled to act, (repeated...) threats of nukes be damned. Europe will not tolerate another Nazi Germany on its borders, period.
Put another way, a massive, discontinuous step in escalation will inevitably lead to a similar step from the other side. There is no world in which Germany and Poland go "OK then" and withdraw all aid.
Of course there is. Mass mobilization and a war economy would do the trick. Many of Putin's rivals are calling for exactly that.
Ukraine's military barely held on against 90k professional soldiers and 140k mobilised. It would not stand a single chance against 3 million soldiers and a fully militarized Russian economy. Russia hasn't even called up a tenth of its trained reserves.
Destroying the pipelines removed the potential reward for an internal rival to replace him.