At what point did the USSR become non viable? Economically speaking many viewed it as a ticking timebomb*. To that end how would they have kept it afloat -- they either find something highly desirable in the ground in a place they control, somehow get a massive innovation boost, somehow morph into maybe not a post scarcity society but something closer to it than not (very very cheap energy say). That is probably not really worth considering beyond sci fi stories so I can't do that. Others have argued it is fundamentally against the nature of human society, I am less sure of that but at the same time they did not do well on the humanity front.
*a lot of economic development happens at the cost of the environment, you can however also spend your population and the USSR was right into that. Equally if you have never read about so called economic hitmen then go have a look (confessions of an economic hit man being the starting point for most people looking into it) and though most there look to undeveloped countries there was enough stuff going on in the USSR and its territories.
But OK so the USSR does not collapse at the end of the cold war but at the same time sorts it out enough to continue on as it was (it functioned for between four and seven decades, we are now 25 years on so 25 more years could kind of work), all the same states as they were, not enough manpower to take over any other countries and keep hold of them. Would the cold war stay cold, I would go with mostly and just leave it at proxy wars in Africa, the middle east and likely parts of Asia as well. I don't know what inventions or resources would not have made their way onto the open market. Equally I am not sure what the US would be like as a general concept -- though a lot of the anti Russia (give or take this last 3 or so years) was mostly seen as a thing for old people to worry about we see the legacy of the effects of it to this day (socialist being a dirty word in US politics). Would the propaganda bubble have burst like it did, maybe a few years down the line, or would it have galvanised things even more? What would China's place in the world be, relations between USSR/Russia and China kind of soured in the 60s at the latest and more like the 50s for most things. Either way it was a bit of a rift that formed long before the end of the cold war. On the other hand the energy that fuelled China's growth post 1990 was largely from Russia and I am not seeing many other places for it to come from so who knows.
http://www.tradingeconomics.com/china/exports has Russia as a bit component but hardly all of it.
The proxy wars thing would be interesting for me -- Russia was the reason Syria did not kick off quite as soon as it did thanks to historical ties (and it being one of the only "warm water" ports that was friendly with Russia). With that in mind I imagine the middle east would be rather different today, and though most of the problems many would instead look to the end of world war 2 to point fingers at (people drawing lines on maps based on colonies/empires/because it is easy with no great for historical or ethnic or religious concepts) the cold war did not help things. At the risk of being a cynic the US does seem to operate on fear so there would probably always want to be something. Whether the US and Russia would continue supporting less than stellar governments because they claim a certain dislike for a given ideology. With that in mind I imagine Africa actually dodged a bullet there in some ways as it was the next best choice for a sandbox to play in.
The fall of the USSR was certainly not a bad thing from where I sit, though it could have been handled more gracefully, and ultimately made the lives of a lot of people a lot better. At the same time though I don't think we would have seen world war 3 or a takeover or a marked drop in science/tech development.