Genuinely curious, what alternatives were there in the 2000s? Did dependency on Russian gas doom German manufacturing or did it provide it 20 additional years of artificial life support?
Nuclear. The Schroeder government initiated the German nuclear phase-out (which was later reverted and re-reverted by Merkel). But rumor has it that the nuclear phase-out wasn't only motivated by the greens being anti-nuke, but also by Schroeder being interested in pushing gas instead.
Btw., after his chancellorship, Schroeder got a post at the Russian state gas supplier Gazprom.
His direct involvement with the Russian oil and gas sector (and, most likely, influence on their behalf) is a lot more recent than just 'the 2000s' [0][1].
Diversifying just a little bit would go a long way.
When Russia invaded Ukraine suddenly several LNG terminals gained regulatory approval, even though previously those projects were in bureaucratic purgatory for years.
Btw., after his chancellorship, Schroeder got a post at the Russian state gas supplier Gazprom.