Putin is in a political hot mess in Russia.
Many highly placed Russians want his head on a pike (some are dying for thinking that way). It is in Vlad's best interest to take Russia's leverage (pipeline valve) away (much like burning the ship that got you there).
His internal detractors would love to take him out, negotiate forever on some deal with Ukraine and make nice with Europe - "Oh Vlad was so bad and he'd be happy to make nice with Ukraine if he were available, and we of course will help Europe in its time of energy need with our handy pipeline".
That option is now off the table. Vlad is now much more safe. Not even Vlad's internal detractors would rat him out for taking out the pipeline. Once exposed, they'd be dealt with and due to the new circumstances, all of Russia is (now) more committed to being alienated.