Assuming the Soviet Union remained an entity to the present day what kind of nation would it be? Still a superpower? Would China sill have risen like it did over the last 30 years?
It really depends on exactly how the Soviets have survived. Almost certainly even a "stagnant" Soviet system would still host a dynamic society inside it and be surrounded by a dynamic world, so even a zombie Soviet Union would not be the same country in 2020 as it was in 1985.
Potentially, things could be pretty OK. No collapse means no collapse of the Soviets health and education, and that's really good for the region. The region's demographics would be massively improved. The long oil price low in the 90s might mean that the Soviets finally transition from a coal-powered economy to an oil and gas powered economy (which would bring enormous efficiency gains). Relations with China are likely to continue to improve and in the 21st Century this would mean that the Soviets have a friendly peer economy to trade with for the first time in its history. Trade and technology trades with China could boost economic efficiency as well.
On the environmental side, a continuing Soviet Union would mean that environmental disasters could be better controlled (I expect the Soviets could avoid the decay of cotton farming in Central Asia that resulted in actual slave plantations accelerating the already bad situation, for example). On the other hand, the Soviet "war against nature" will continue and there will be no fall in CO2 output from Soviet industry ending. So on the local level, things are better, but for the world things are much worse. The Soviets likely do some degree of water diversion from the north - at least diverting water from Russia's Arctic wetlands to feed the Ukrainian farms.
Possibly the Communists also co-opt their nascent environmental movement, cloaking their difficulty in competing with the West as virtue and making the Capitalist world's "war against nature" even worse as in the West environmentalism becomes linked to Communism.
Human rights abuses continue. Opponents to the regime are likely to continue being treated as mad. Religious freedom continues to be restricted. Some nasty racial tension could develop between Central Asians and the Slavic populations of the Soviet Union as the union becomes increasingly Muslim and Altaic as the demographic gap between the richer republics and the Central Asian republics starts to become noticeable to the ordinary man on the street.
Immigration, especially from Vietnam, likely continues. At some point the Soviets will probably need to admit that these guest workers are permanent additions to the Soviet population, not short-term loans.
The Cold War continues, human civilization continues to be very aware of the sword of damocles above it. I am dubious about how much further arms control talks could go in actually reducing risk while the Soviets are still ideological opponents for the US. There might be some success in preventing an expensive arms race in orbit. The Soviets may face some discomfort as China rises - becoming more of a competitor for title of top dog in the Communist world. Alternatively, a continuing Cold War may cause Sino-American relations to crack earlier, leading to a renewal of the strategic partnership between the Soviets and the Chinese. Alternatively, a continuing Cold War might mean the US works harder to keep China on their side, meaning an even faster rise of China.
Things could get interesting in the 3rd World Soviet allies - 40 years of burgeoning global trade due to China rising (to whatever degree it does rise) and continued Soviet subsidies and security guarantees could lead to the emergence of Soviet-aligned middle income states that are actually worthwhile trade partners. I tend to think that while a continued Cold War would not lead to such a precipitous fall in violence during the 90s, decolonization being mostly complete at this point likely means the 3rd World is nonetheless more calm than it had been in earlier eras of the Cold War.
The Soviet Union would, in military terms at least, still be a superpower.
That's the "plausible optimism" scenario as I see it. Things could be quite a bit worse. Humanity could also be extinct. There's a range of options.
fasquardon