All SSRs broke with Russia (even through the Central Asian didn't want to), because de jura they were independent state in common union. The ASSRs stayed part of the SSR they were under.
So you would just need some of the former SSRs to survive, or some of of the ASSRs to become SSRs.
The Karelo-Finnish SSR is one of the most likely to survive, as it only was demoted in 1956.
The Volga German ASSR could potenial had been promoted to a SSR before the war and accidental survived. Beside that we have the Caucasus ASSR as some which could have been promoted, through none beside Dagestan are truely viable. Crimea could also have become a separate SSR rather than a ASSR. There was discussion to establish an Siberian German ASSR or SSR from Kazahkstani territory in the late seventies and eighties. Kaliningrad would have made perfect sense to make into an SSR based on geograhic concerns (it could also had been transferred to Lithaunia under the 1956 territorial reforms), but usual the Soviet needed some kind of ethnic excuse to make an SSR.