The fundamental contradiction between the working class and the owning class (over maximizing vs minimizing wages) continues to exist, which means that any system that tries to manage that contradiction can't be permanently stable. Social democracy is the best known and most successful strategy for managing class conflict, but in the US and UK it was only fairly stable while the USSR meaningfully threatened to overtake them economically, and collapsed completely when the USSR did. It has lasted longer in Europe, but has clearly also been in decline since the 90s, with various governments resorting to "austerity" or having it forced on them.

I still question your claims of cause and effect here. The US abandoned this well before the USSR had fallen, and the reason the rest of Europe followed suit was not the fall of the USSR, but merely because they were blindly following the US, which they saw as a leader in this matter.

But plenty of countries did not follow down that part. There's no reason to assume this can't be stable, but you do need to limit the influence of big money and neoliberalism on your society.