I really liked this question, and was hoping that a Soviet expert might come along and answer it. Perhaps they still might, and I’m sure will do it better than I can, but in the meantime I can give a partial answer based on some knowledge of certain Soviet institutions of the period (chiefly the Comintern) and relying heavily on a book I really like: Sheila Fitzpatrick’s Everyday Stalinism: Ordinary Life in Extraordinary Times: Soviet Russia in the 1930s (OUP, 2006). One aspect of this question – what proportion of the Soviet Communist Party were arrested, and how many of these were killed – I am going to leave alone, as the debates about enumeration are beyond my ability to evaluate. However, hopefully I can give an idea of the threats your fictitious communist might face, and what they might have been able to do to try and avoid death by artificially-induced brain haemorrhage.

One thing I liked about the question was that you used ‘1930s’ to frame it, not just the Great Purges of the late 1930s (chiefly 1937-8). This may or may not be intentional, but it’s a useful reminder that the history of Stalinist purges has a fair bit of backstory leading up to this point, which is quite relevant to the question at hand.

The Soviet Communist Party, after all, had been in the business of purging itself for a few years before 1937, and the persecution of various categories of class enemies (kulaks, priests and other formerly privileged elements of society) had been going on for even longer. Soviet leaders had always had an eye to revolutionary history, they knew that revolutions always have enemies waiting for their chance to strike, and the utmost vigilance was required against them. Initially, purges (small-p) of the Party had been a matter of inward concern about composition – was the Party working class enough? Had undesirable elements managed to obtain membership? Being a member of the Party required submitting oneself to close scrutiny, aspiring members filled out detailed autobiographies of their personal and social history, which were updated periodically, and could in turn be used as the basis for judging their status as members. As Fitzpatrick notes, efforts to purge the Party of ‘undesirable’ members became almost an annual process from 1933 onwards, growing more and more vicious. By 1936, 9% of those expelled from the Party were also arrested (c. 15,000, just to give an idea of scale), generally as spies, kulaks or similar. But by this stage, death seems to have been a relatively rare outcome, although the advent of Show Trials in 1936 – initially tied to Kirov’s 1934 murder – certainly had deadly outcomes for the accused. But for the middling-level Party member of your question, the question was not yet one of life and death. Moreover, the Party purges were, by the regime’s standards, logical and based on concrete grounds – if you were of impeccably working class or peasant origins, and had never held political positions that could be construed as opposed to Stalin, you were on safer ground. Let’s say your hypothetical communist ticked those boxes.

Yet the ‘success’ of these purges created their own problems. For one thing, they had created a new class of enemy – expelled members now outnumbered actual members in some regions, and by Stalinist logic these were now assumed to be enemies as well. More fundamentally, after years of persecution, class enemies had learned to bury their pasts and adopt working-class identities. Party members had learned to be circumspect about any political deviations. If communists could no longer openly disagree, how could you tell what they were really thinking? The paranoia of the Stalinist regime, hitherto directed towards certain categories of external enemies, was now increasingly focused on imagined enemies within. With the criteria of defining ‘enemies’ now rendered obsolete, accusations, suspicion and consequences had become untethered to logic, even by the regime’s warped standards. Purges, from now on, were much more random. Just because you kept your head down and didn’t contradict the Party line didn't guarantee your safety any more.

Working in your Party member’s favour was the focus on the elite of the Party, not just Old Bosheviks tried and executed over Kirov’s murder, but from early 1937, mass arrests and trials of regional and industrial officials accused of ‘wrecking’– as Fitxpatrick put it, ‘it was the whole Communist managerial class that was now on trial.’ (p. 196). These were Party members who had done quite well out of communism, mismanaging state projects, misusing funds and creating their own empires of influence. Soon, other privileged members of Soviet society – in government, the intelligentsia, foreign communists working for the Comintern, the armed forces – came under similar suspicion over the course of 1937.

Yet despite the focus on elites, your friend still faced several sources of danger. For one, he may well have had friends, family or associates who were higher up the chain – and if they became ‘enemies of the people’, then their associates also became objects of suspicion, especially if the accused was ‘pressured’ into revealing their ‘collaborators’. This was especially problematic as earlier strategies to avoid political threats relied heavily on being part of these very networks of patronage, and these new purges turned many Party members’ first line of defence against accusations into a liability. They had also better hope that they don’t have any personal or professional enemies, no one who might want to publically denounce them, or even be willing to point the finger purely to shore up their own position. They might even be tempted to do this themselves, but this might carry its own risks as the purges wound down and excessive behaviour was punished. Internal Party elections mandated in spring 1937 might also be a source of concern – branch officials were required to be re-elected, without the usual central ‘lists’ provided to ensure that the favoured candidates were duly put forward and elected. Without lists, there was a need for many more candidates, and for careful discussion of each to narrow down the field – with the presumption that at least some of them would thereby be exposed as ‘enemies of the people’. Also remember that there was an inescapable side effect of the purging of Communist Party elites, especially given how intertwined the Party was with state institutions: social mobility. With so many of their superiors arrested, imprisoned or dead, it might be quite hard for your communist to stay safely in the middle of the pack, although it wasn’t unknown for Party members to refuse promotion for this very reason – safer to be at the bottom.

So, depending on the survival strategy employed, they might have quite decent odds of avoiding suspicion, but by no means a certainty and certain strategies that worked well at first might backfire later – and some strategies required having acted in a certain way years before the purges even began. In other words, while it might have been possible for them to try and minimise their risks, it would have been near impossible to remove the risk altogether.