So, how hard was leaving USSR without being part of the party or being in a mission or something like that? Even if a soviet person was allowed to apply for a leaving permit, what was the chances of them getting one?
Do you have a specific time period in mind? The answer will be different if you're thinking of the 1920s, 1940s, or 1980s.
I was going to write a bit on what was likely in the 1960s-1980s but I just wanted to check that that was what you were interested in.